Use glyph metrics for spacing.

The CharacterSpacing property of Font can be used to add additional spacing
between characters and is by default 0.
Use glyph metrics for white characters.
Increase GPB minor version because of changes in TTFGlyph.
Read and write array of TTFGlyph platform independently.
Merge pull request #1518 from michalsrb/next

Use glyph metrics for spacing.