Added action line drawing.
Added MM8BDM palette by request.
Made action lines optional.
Used ? for thing sprites in configurations.

This should make it friendlier to TCs and mods which may not use the
same mapping as the IWAD does. (E.g., KDIZD's Hell Knight uses BOS2A1
instead of BOS2A1C1.)
Added Zeth nostalgia mode.

Well, not really. It's just that you can choose to use Zeth icons
instead of Slade icons for those things that have them.
Map format-dependent specials in configurations.

It's a bit of a heavy-handed hack, but it works. Now the ZDoom config
can properly support Doom format maps as well, without losing support
for Hexen and UDMF. It'd probably be better to do that with namespaces
rather than map formats, but it can wait I suppose.
Configuration update, flags and sector types.
Config update, ZDoom specials in Doom format.
Added a non-zero check for tags.

Used a macro to make all these checks cleaner and less repetitive.
Adding "&& tag != 0" everywhere gets old fast.
Merge pull request #65 from Gaerzi/master

Sync with my fork.
- Don't draw action line if the tagged sector of a line special is adjacent to that line
- Made the arrow lines a bit thinner
Make jpeg image format valid for texturex patches
Tweaked the look of vertex hilight/selection overlays (when point sprites are enabled)
Merge branch 'master' of https://github.com/sirjuddington/SLADE into osx