Be more consistent with error handling.

Let apps handle errors from the serializer. They probably want to log
the exception and continue.

Moving to branch 1.3 because this is a backwards-incompatible change.
One more log fix and CHANGES.
Pre-release for safety/testing.
Match urls case-insensitively
Add case sensitivity test.
Update changelog.
Accept double-quote in CSS values.

From 0df7b58 by nickburlett. Fixes #82.
Added install method to README.

Fixes #83.
Fix up docs.
Handle markup within <a> tags. Fixes #80.
Document attrs callables. Fixes #77