Fixes documentation 

See related discussion #49.

 - Added french translation for intllib

also, setting an avoid radius would be a good idea.

with model changes by VanessaE

Switch `add_node` to `set_node`

Update and rename flowers_plus/textures to flowers_plus/textures/tr.txt
Update and rename bushes_classic/locale to bushes_classic/locale/tr.txt

don't actually run the checking loop if there's nothing to do!
otherwise it spins the CPU at 100% for no reason

if there is time to do so (up to a max of 0.2 seconds' worth)

This prevents unpopulated map areas being left over after a restart.

Adds a fairly large shutdown penalty to the engine only if the mapgen is
actively generating at the time of shutdown.  If the mapgen is more or less
idle, no extra time is added.

instead of manually searching for air above find_nodes_in_area() list

This allows to dig doors or other snappy blocks you own.

fixes two minor issues:

-sickle didn't respect protection for grass or wheat
-sickle added wear even though the item wasn't diggable

Fixes a bunch of issues with the sickle:
-sickle didnt care of protection
-sickle removed filled chests (also locked ones)
-when applying to a dirt node thats not "under" a player, the grass got added to the wrong position
-everything that was above a dirt_with_grass node got removed

Now I am proud to announce, that all these issues got resolved.

fix wrong use of near_nodes_* fields in willow def

(rather than always the first found)

move API.txt into plants_lib dir
moderate re-formatting of API.txt, accounting for tab width = 4 spaces.

(requested limit is 0.2s, but actual tends to be around 1.5s max lag spike)

new texture filenames also.