Cargoify servo
Merge pull request #3230 from servo/cargoify

Cargoify servo
Update the README a bit.
Merge pull request #3259 from metajack/update-readme

Update the README a bit.
Improve quality of font rendering on Linux (and Android).

The freetype hinting only works on integer pixel sizes. For this
reason, the advance width metrics for a font of size 12.99 are
the same as the advance metrics for a font of size 12.0. This
results in small fonts appearing to overlap slightly, which is
particularly noticeable on parts of Wikipedia. Round the font
size up to a pixel boundary inside the freetype system.

Also fetch the system default fonts for the generic font families
rather than hard coding them.

These two changes make the font rendering on Linux very close
to the Firefox font rendering on Wikipedia.
Define constant parameters strings as statics.