Add notice regarding Twill, and skip test_examples
Add flexibility to parseLinkAttrs

Add more code to decode the input HTML as string, and add a parameter
to allow an error (e.g. in decoding) to produce an empty result rather
than throwing an error.
Add docstring
Enable fetchers' responses to decode themselves

In fetchers.HTTPResponse, try to decode response body as a string
based on charset in the content-type header, if available. Also add
tests for utility functions, and update tests for the case where
the response body is decoded as str not bytes.
Remove unused imports
Code style updates