support altering quality without specifying format
refactor tests

- Make many tests more unity, directly calling the methods they are designed to test and testing for specific return values and side effects and group them together
- Make tests pass for dprs other than 1
add fresh built files
fix up a couple more tests
Add more info to changelog
Merge pull request #247 from mobify/v2.0-quality-without-format

support altering quality without specifying format
Merge remote-tracking branch 'origin/v2.0' into v2.0-umd-browserify

Conflicts:
	build/mobify.min.js