2.0.0-alpha5

This is the fifth alpha release of our 2.0.0 "dev builds".

The old stable v0.18.2-rc1 release still has more optimized output for Q1 and faster/less memory use for qbsp/light, but we're working on regressions and welcome feedback as we work towards a stable 2.0.0 build.

Fixes since alpha4:

• qbsp: fix for Q2 animated textures
• qbsp: fix leaks through detail in LibreQuake e3m4.map
• light: fix entire lightmap turning black in some cases when using _surface lights
• light: fix excessive bouncing with lit water, or _shadow -1
• lightpreview: don't crash when vis is run more than once

Enhancements since alpha4:

• vis: more performance (gmsp3v2.bsp vis, 32 threads: 18.2s -> 10.6s) (@rrika)

Additions since alpha4:

• qbsp: add -missing_textures_as_zero_size flag to allow writing 0x0 textures
• lightpreview: bind arrow keys / pageup / pagedown in addition to WASDQE (@maikmerten)
• lightpreview: add support for fence textures (#402) (@dsvensson)
• lightpreview: frustum culling and cull freeze (#398) (@dsvensson)

Other notes:

• VS runtime for the Windows builds: https://aka.ms/vs/17/release/vc_redist.x64.exe
• Documentation is now at: https://ericw-tools.readthedocs.io