Add mgv6 spflag 'flat'
Global flag is kept for backwards compatibility but is now undocumented

Increase default from 6 to 16 to help with mgv7 and mgfractal
Large-scale or alternative mapgens can result in a lowland spawn point not
being found, causing a spawn at (0, 0, 0) possibly buried underground
The max height is now settable to allow correct player spawn
in any mapgen or when using custom noise parameters

* Add key settings to setting table and ignore them later
  This way they are added to the auto-generated minetest.conf.example
* Add flags type
* Add input validation for int, float and flags
* Break in-game graphic settings into multiple sections
* Parse settingtpes.txt in mods and games
* Improve description for a lot of settings
* Fix typos and wording in settingtypes.txt
* Convert language setting to an enum

Settings are automatically parsed from builtin/settingtypes.txt
The edit dialog automatically adjust based on the type of setting

- Add warning log level
- Change debug_log_level setting to enumeration string
- Map Irrlicht log events to MT log events
- Encapsulate log_* functions and global variables into a class, Logger
- Unify dstream with standard logging mechanism
- Unify core.debug() with standard core.log() script API

Preserves the rare unbroken protruding dungeons
Fix random range for first room roomplace
Fix checked volume for first room 'fits' bool
and check for 'untouchable' flag instead of 'inside'
Remove 'enable floating dungeons' setting

Enable the server to request the client to reconnect.

This can be done with the now extended minetest.request_shutdown([reason], [reconnect]) setting.

Mgv6: Enable snowbiomes by default. Double biome noise spread. 3 octaves, 0.5 persistence for humidity

Due to compatibility concerns, this is temporarily disabled.

Now matches function comment

Remove dynamic weather year parameter