Custom pytest assertion comparison for RevisionSet

http://pytest.org/latest/assert.html#defining-your-own-assertion-comparison
Make RevisionSet possible to be copied
Merge function for RevisionSet objects
Merge branch 'feedlist'
Merge branch 'feedlist'
Fix bug when decodes named timezone.
Unify get_parser into get_document_type
Rename num_of_thread to pool_size
crawler returns feed url as well
category with no term will not be parsed
Fill required date time attributes if not present
id and link self tag is required when parse RSS2 feed
Rename data_for_crawl to crawler_hints
Type of RSS2 content is html
Compare date time attributes with date time objects, not using decoder
Use == operator when compare int
PEP 8
Merge branch 'master' of https://github.com/earthreader/libearth
typo
Fix bug fields empty if DocumentElement is Child