Adds kerning property to BitmapText

Author: wtravO

CHANGELOG.md

@@ -19,6 +19,7 @@ being passed to the simulation. The default value is 1 to remain consistent with
 * HTML5AudioSound.setVolume is a chainable way to set the volume of a single Sound instance.
 * HTML5AudioSound.setSeek is a chainable way to set seek to a point of a single Sound instance.
 * HTML5AudioSound.setLoop is a chainable way to set the loop state of a single Sound instance.
+* A new property was added to BitmapText, 'kerning' which accepts a positive or negative number to add/reduce spacing in between characters.
 
 ### Bug Fixes