few small updates

- wording improvements
- replace "readily available" with "first text-paint-time"
- fix "timeout" -> "font-timeout" in examples
- add CSS highlighting
font-desirability: optional, progressive, mandatory

Reworked font-desirability to provide hooks for first paint rendering strategy.

closes #1, #4
fix section heading levels
switch to font-rendering
make <time> optional, default to 3s
fix desirability references
moar better english
Opera matches Chrome

This makes sense, since both are Chromium-based.
Merge pull request #1 from mathiasbynens/patch-2

Opera matches Chrome
specify default strategy if font-rendering is omitted
Update README.md
Merge pull request #2 from okize/patch-2

Update README.md
fix typo
Merge pull request #3 from scheinercc/patch-2

fix typo
Merge pull request #5 from igrigorik/patch-1

font-desirability: optional, progressive, mandatory