Add changelog
Bump version to 0.2.0

Fixes #19.
Merge pull request #25 from chiphogg/changelog

Add changelog
Add 'clear_bg' flag to output cleared bg

This way we don't have to worry about precisely matching the background
colour; close enough is good enough (as long as the text colours still
look good).

Fixes #26.
Merge pull request #27 from chiphogg/clear_background

Add 'clear_bg' flag to output cleared bg