Added whole-pixel text rendering.

Fixed what looks like the last bug in sub-pixel rendering, which was
incorrect clamping (one texel too short on the high end).

Glyph texture atlasses are now 256 x 256 pixels.
Android text rendering is working.

Also, changed the style resolution stack so that
there is a pool per stack level. The previous design
would have grown the pool indefinitely, for every new
element that was styled.