* 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

This feature is still experimental and has some issues. Also,
increase texture_min_size to 64 px. The setting was initially
a conservative 16 so that the effect would not be noticable
for players who aren't using aniso/bi/trilinear filtering. This
isn't necessary now that texture_clean_transparent is disabled
by default.

Signed off by: Zeno, kwolekr

Conf.example: Update mgv5 mapgen params
Mgv7: Lava caves only below -256

Fix unused (and so, broken) enable_rollback_recording. This option must be reloaded at server loop but loaded when server starts, for data consistency (not a hot load variable)
ok @ShadowNinja

Conf.example: Add mgv7 cave1, cave2 noiseparams
Mgv7: Make skipping of mountain code relative to y=0 not water level
Mountain noise offset now -0.6 to compensate
Tune chance of large caves