backends: Make search/find_exact take a query dict instead of kwargs
backends: Make search/find_exact accept 'uris' kwarg
core: Limit search to backends matching URI roots

Fixes #337
docs: Update changelog
Merge branch 'develop' into feature/limit-search-by-uri-root

Conflicts:
	docs/changes.rst
Merge pull request #364 from jodal/feature/limit-search-by-uri-root

Limit search to only return matches within given URI roots