MAIN: Don't give gamma a default value of 1.0

It now defaults to using whatever the system has
AURORA: Check for divide/modulus by zero
COMMON: Add int32 min/max defines
AURORA: Check for quotient overflow in the int/int case of o_div
AURORA: Check for modulus by negative numbers
AURORA: Check for either arg being negative in o_mod
DOCS: Mention the mailing list in the README
Fixed compilation error.
Merge pull request #16 from ImperatorPrime/master

AURORA: Fixed Compilation error.
COMMON: Make sure INT32_MIN and INT32_MAX are signed
AURORA: Add ResourceManager::blacklist()

A blacklisted resource will never be used.
ENGINES: Bump the base resource priority to start at 1

Because 0 now means blacklisted
NWN: Blacklist fnt_galahad14.dds, fixing Cyrillic fonts

This closes issue #15.
DOCS: Mention the wiki TODO page
GRAPHICS: Also do 16bpp video modes
MAIN: Make the target command line argument handling less ambigous

Now, if a non-existing target is specified together with a path,
xoreos will create that target.
DOCS: Mention the project wiki
NWN: Mark the "portraits" data directory as optional
GRAPHICS: Import updated YUV code from ScummVM

Bink and XMV now have improved contrast
DOCS: Fix a few small Doxygen issues