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

Conf.example: Correct grammar and spelling. Shorten some lines. Move a few lines into correct sections. Remove finite liquid reference. Make indentation consistent

Increase indentation throughout file for clarity. Correct mistakes. Shorten lines. Make more consistent

Signed-off-by: Craig Robbins <kde.psych@gmail.com>

Signed-off-by: Craig Robbins <kde.psych@gmail.com>

If liquid_queue_purge_time == 0 then disable the queue size limiting and make this the default setting
Additionally, liquid_loop_max now defaults to 100000

Add format example to minetest.conf.example
Add Settings::setU16()
Throw exception on attempted access of NULL settings groups

Fix non coding style conforming glb_fontengine to g_fontengine
Fix fonts never been deleted due to grabbed to often

Signed-off-by: Craig Robbins <kde.psych@gmail.com>