Fonts consist of
  fontname.fnt
  fontname.png
and you load fonts by just specifying the "path/fontname" part.

The .png is an 8-bit greyscale image, used for alpha-blending the text.
(DXTC allows 0.5 bytes/pixel at best, which isn't much better than
PNG's 1 byte/pixel, and DXTC's lossiness is almost noticeable,
so we stick with lossless formats.)
Or it's a 32-bit RGBA image, to allow more complex text styles.

The .fnt file is something like:

  101
  512 256
  a
  3
  16
  12
  32 0 0 10 10 12
  33 10 0 6 10 7
  3300 16 0 6 10 7

First line = version number of file, for slightly better error
detection if people leave old ones hanging around.

Second line = size of texture (width/height).

Third line = texture format: "a" or "rgba".

Fourth line = number of glyphs in the font.

Fifth line = line spacing (pixels between each baseline)

Sixth line = text 'height' (height of the "I" glyph, possibly manually
                            adjusted so that vertical centering works)

Each subsequent line is

  <code point> <x> <y> <width> <height> <x offset> <y offset> <advance>

0 <= Code point < 2^16.
x, y, width, height are in pixels on the texture.
x/y offset are the position of the texture relative to the glyph's origin.
advance is the number of pixels to move along for the next character.