Add clear
Merge pull request #23 from sanxiyn/clear

Add clear
Factor out CssStylesheetParams and add parse_style_attribute.
Include style attributes in selector matching.
Merge pull request #24 from metajack/style-attribute

Implement style attributes
Update tests for new select_style signature.
Merge pull request #25 from metajack/select-test

Update tests for new select_style signature.
Update to latest Rust
Merge pull request #26 from kmcallister/rust-upgrade

Update to latest Rust