Add “wordCharacters” as a scoped setting

Set this to a string of which characters should be added to the set of word characters.
Loosen rules about tab trigger boundaries

Previously the character before the potential tab trigger had to be of a different character class. This is now only required when the first character of the tab trigger is a word character.
Allow zooming icon animation to be disabled

To disable, run the following in a terminal: defaults write com.macromates.TextMate.preview fileBrowserOpenAnimationDisabled -bool YES

Closes #109