Add functional test covering default application.
Allow multiple suffixes for a single type name.
Add a test for assertPartialDict() for good measure.
Test the script_name and path_info are as expected, too.
Add tests for URI-based matching.
Add parameters on aliases for testing purposes.
Add functional tests on content-type header.
Add functional tests on accept header

This excludes testing the best-match algorithm.
Replace 'suffix' with 'suffixes'

Since the type suffixes are now represented by a list, change the
key for them to the plural form 'suffixes'.
Rename 'aversion.content-type' to 'aversion.content_type'

This change is motivated by a desire to maintain consistency
with the other variables set by AVersion.
Update the documentation

This includes updates to describe aliases, parameters on
versions and content types, the WSGI environment variables,
and the "overwrite_headers" configuration.