Added custom IEqualityComparer to SpriteFont glyph dictionary.
Replaced internal _texture access.
Removed _characters in favor of auto-property.
Simplified logic around missing glyphs.
Removed always true if statement.
Merge pull request #2604 from SickheadGames/fonts

SpriteFont Optimizations Pt. 1
Merge remote-tracking branch 'upstream/develop' into develop