Consider adding support for OTF OpenType fonts

[mdtauk]

Whilst exploring using the font tool to generate Japanese font textures, I am running into an issue where modern OpenType fonts use opentype features to support Half Width characters, is required to fully cover all the characters needed for Japanese font replacement.

I can also see it being an issue should modders want to add language support for non Latin alphabets in the future.

[mdtauk]

For implementation, you could maybe parse the codepoints txt file, with comments like

# Opentype --HalfWidth
A
B
C
D
E
...
# Opentype End

Just to clarify, the HalfWidth use the same codepoints as the FullWidth glyphs, except you turn on an OpenType feature and it substitutes the glyphs for the half width ones. So to generate these half width texture images, you would need to activate the feature, and add those same characters to the TXT file.