Moved to refcontext
refcontext works with numeric labels
Updated doc for sortcites
Removed reencode
Correct bibheading levels for memoir (article)

Using memoir, the sectioning hierarchy uses \chapter as the top level
even in article mode. Hence, the top level bibheadings for memoir
(article) must be chapters instead of sections (and create chapter toc
entries), and the subbibheadings must be sections instead of
subsections.
merge from dev