Only render a null glyph once, instead of once per missing character.
Texture size, number of characters/glyphs refactored into enums/variables.
Strings (UTF-8) instead of const(char)[] (ASCII) in the API.
Minor doc fix.
Optional font texture size parameter for init.
Explanation of character count and font texture size.
Using const(char)[] instead of string in the API.
Very minor doc readability improvement.
Fixed a bug in imguiSlider.

`msg` contained an invalid UTF sequence since the entire `fmt`, not just
the result of formatting digits, was formatted into `msg`.
The demo example now shows a use of Unicode characters.
Merge pull request #2 from kiith-sa/unicode-support

Unicode support