Make FWallCoords' members lowercase

because they're kind of a pain to type when all uppercase.
- Also, make its sx1 and sx2 members shorts, so it takes less space, since
  it's getting crammed into a vissprite now.
Redo lighting for each wall sprite

- Because previously it just reused whatever the most recently drawn wall
  used.
Use wall sprite Y scale
Fixed: Wall sprites cut off one pixel short of the window's right border
Skip neardepth/fardepth checking in R_DrawSprite

- Wall sprites now clip much, much better than before.
Parse more info from Blood's map header
Eliminate extra vars from FWallCoords

- cx1, cx2, cy1, and cy2 are not used anywhere, so get rid of them.
- Also annotated the comments to indicate the corresponding arrays in the Build engine.
Don't clamp SHADE2LIGHT

- Light levels aren't stored in bytes anymore, so there's no reason to
  clamp it anymore when loading Build maps.
Merge branch 'master' of github.com:rheit/zdoom