Font improvements to atlastool

This may not be perfect, but it works and we can try it.

What I'm most worried about is the height metric.  Not sure what's best for that number...

Anyway, this makes the following changes:
 * Outputs to stderr for glyphs that are missing when generating font.
 * Improves performance in some hot areas by a bit, since I made it slower.
 * Supports multiple font files/ranges/sizes per font name.

The basic idea is you put this in your script:

```
font UBUNTU24 PrettyFont.otf UWkhcGR 24
font UBUNTU24 CJK.otf cTK 24
font UBUNTU24 Arial.otf UWkhcGR 24
```

Since they are all named "UBUNTU24", it will run through each font (in order) and select the glyph from the first font that has it.  If none have it, the last font with the range is used.

Sizes and ranges may be different for each file.

-[Unknown]