Use new xml-conduit based parser.

Removed old hexpat-based parser and hexpat cabal flag.
Revert "Removed old experimental directory."

This reverts commit 00ad0521f6bdaf1c4c377be47e97688a8303f3fd.
Code in experimental to check new parser against old.
Removed experimental.
Merge branch 'newparser'
Removed obsolete Pickle module.