#2 More robust method for specifying character sets

[Fletcher Dunn]

Need to be able to specify arbitrary subset of characters, not just a range.
* Character set is represented as a list of continuous, non-overlapping ranges.
* Buttons to add/remove a range of characters.
* An "auto" button which will automatically scan the font and detect which characters it actually defines and sets the range.
* Ability to add characters from an external file, with specified encoding (UTF-8 or UTF-16)