Currently translated at 99.2% (276 of 278 strings)

This might break some mods, but it is important for all uses of the param2 to
be documented.

This doesn't need a serialisation version or network protocol version change,
as old clients will still work on new servers, and it is bearable to have
new clients getting non rotated plants on old servers.

Major refactor of emerge.cpp and Map::init/finishBlockMake

It returns the index used in mg->biomemap for a given biome name.
The biomemap is useless without this unless you re-register all existing biomes,
which could cause problems for anyone else trying to use biomemap.
With this, you can quickly create a lookup table of ids and names.

Also add PATH_DELIM for Windows compatibility.

Get facedir by using lowest 5 bits of param2 and limiting to 23
More robust, frees up higher param2 bits for other uses
Change lookup table and table index to u8

-> Remove memory allocation bugs
-> Merge changes from upstream, enabling customizeable memory allocation

1. Check for entity addition success in spawn_item implementation
2. Check for success in item_drop callback, so that the player
doesn't lose the item if they are outside bounds and try to drop it.
3. When existing player joins game, check that their position is inside
map bounds. If not, set their position to the return value of findSpawnPos().
4. Make findSpawnPos() respect the border

2 fixes a lua crash if a player drops an item outside map bounds.
3 fixes an assertion crash if a player leaves when being outside map bounds,
and then rejoins.

Because the count is serialized as u16, this would cause overflow.

If minetest later deserialized a mapblock with an incorrect
static object count, it would be unable to find the NameIdMapping
(which comes after the StaticObjectList) and abort with an error
such as "Invalid block data in database: unsupported NameIdMapping
version" (issue #2610).

Sidelen larger than 16 is essential for low density decorations
With sidelen > 16 chunksize may not be divisable by sidelen if
chunksize is changed, in this situation setting sidelen = chunksize
is desirable and should not create error messages.

Change a remaining assert(0) call to FATAL_ERROR(msg).
There was a regression since commit

ced6d202 "For usages of assert() that are meant to persist in Release builds (when NDEBUG is defined), replace those usages with persistent alternatives"

where when an "uncatched" exception is thrown inside a "side thread",
the program doesn't abort anymore.

This led to the problem @netinetwalker experienced where the emergethread
got an unhandled exception for loading a mapblock while redis was loading,
(see #3196) and then jmped outside its loop to work down its queue.
This resulted in the server not doing any emerges anymore.

Thanks to @netinetwalker for spotting the error, proposing a fix, and testing it.

Error due to @est31's merging changes to PR #3202 to add more error reporting for invalid reply types, commit:

524a7656 "redis: throw error if block request failed"

Now we branch out on the valid reply type "not found".

For example, on Fedora systems jsoncpp headers is installed in `/usr/include/jsoncpp`.

On world load the collision code can not see node boxes, since the
nodes have not been loaded. Thus it collided only at the next full
node. However, standing on a slab on world load leaded to sinking into
it until the world finished loading. Then one maybe fell further, if
the node below was not walkable.

Now, with this commit, when no node around the player has been loaded
it simply does not move the player.

Because not all circles are round:
* circles using an euclidean metric are what we usually call "round"
* circles using a maximum metric look like euclidean rectangles with equal adjacent sides (squares)
* circles using a manhattan metric look like an euclidean right angled rhombus (squares, but 45° rotated to the former one)

[ci skip]

Update .gitignore to ignore symlinks to non-static Minetest directories and sort into an editor section

[ci skip]

Fixes #3196. Before, we didn't throw an error, and the engine thought the
block isn't occupied. But in fact it might be that redis is still loading,
and the block does exist in the database. The result was a cheesy map.

Why doing things simple ? Use pointer instead of strings to save players and remove them.
Saving players by name does a lookup to find pointer we already have ! Idem with removePlayer
Also remove unused removePlayer(peer_id), it's never called

... and remove trailing whitespace.

Thanks to @kaadmy (NeD) for pointing this out.

-> Don't pass pointer to whole IGameDef to NodeMetadata constructors
	and deserializers, but only to IItemDefManager, which is needed
-> Remove the unused content_mapnode_get_new_name() method
-> Fix style for MapBlock::deSerialize and MapBlock::deSerialize_pre22,
	improving accuracy of error messages a bit
-> Fix style at other serialisation methods too
-> Improve accuracy of some comments

Use std::queue instead of std::set, we don't need such a heavy container.
Don't convert position to int to convert it back to float in the next function.

Document the node metadata changes of the commit (serialisation version >=23):

704782c9 "WIP node metadata, node timers"

The legacy code added in commit

d879a539 - "Add minetest.swap_node"

for sending the whole mapblock to older clients on the case of a node
modification with swap_node, had the problem that the block chosen to be
sent to the client was referenced with node coordinates and not with
block coordinates, resulting in getting the wrong block sent to the client.

Borders have to be converted into BS format in order to be accurately comparable to
object positions.

Entity positions are serialized as F1000. Disallow placing
entities outside safe borders with the minetest.add_entity
call.

Note that this patch only enforces those boundaries for
placing entities, moving entities that move outside boundaries
aren't affected.

Thanks to @nanepiwo for pointing this out.

Remove unusable fine rotation by param2
Remove unused and redundant code
Fix code style issues