Improve consistency of code formatting

This re-formats the code which was formatted differently than primary
way CSS code in Pure.
Merge pull request #81 from ericf/code-formatting

Improve consistency of code formatting
Add CONTRIBUTING.md which documents how to contribute to Pure

The README.md was updated to remove some information which now lives in
CONTRIBUTING.md.

Closes #75
Remove extra space from CONTRIBUTING.md
Merge pull request #83 from ericf/contributing

Add CONTRIBUTING.md which documents how to contribute to Pure
Ignore soon-to-be created folders from Screwdriver CI builds
Clean up misc. formatting, `cursor` and `outline` styles
Clean up Buttons test page to be a very plain HTML page
Add Base to Menus test page
Improve `:focus` styles by making the same as `:hover` styles
Add back `cursor: not-allowed` for disabled buttons
Update styles for focused disabled Menu items to look disabled
Update HISTORY.md entries with more info on `:focus` changes
Merge pull request #86 from ericf/improve-focus

Improve `:focus` styles by making the same as `:hover` styles
Highlight `:focus` styles change in README.md
Bump version to 0.2.0
Bump version to 0.2.1-pre