Merge tag '0.0.5' into develop

Release 0.0.5.
Merge tag 'seams_bias' into develop

0.0.5a
Merge tag 'anim_swim' into develop

0.0.5b
Support floor skies.
Fixed issue with floating texture alignment.
Lighting eqs closer to original.
Implemented shader lighting effects.

This implements all the lighting effects present in Doom 1 & 2 (flash, strobe,
glow, with sector-level syncronisation). The implementation is completely done
in the shaders, keeping the VBOs static.

This commit also fixes a problem which crashed the renderer on E4M7 due to
degenerate polygons after the simplification procedure; this polys are now
simply dropped.
Light param tweaks based or prboom
Added sky rendering.

Figures out limits of sky `super-sector' (i.e. the sector whose sky walls
should block rendering outside of it) and renders the sky as opaque walls using
a new sky shader.
Bumped version to 0.0.6.
Merge branch 'release/0.0.6'

Change log:
* Lighting effects (flickering, flashing etc.)
* Sky rendering.