Add DTD information
Export an XML module
Atom: allow content to be (X)HTML

Fixes https://github.com/Cumulus/Syndic/issues/20
Atom: adjust the unsafe representation for XML content
Atom: allow [summary] to be XHTML
Fix the documentation of [parse] functions
RSS2: take appropriate action when some data is missing
RSS2: be even more flexible with date parsing
Move handle of namespace in generate_catcher
Merge branch 'master' into xml

Conflicts:
	lib/syndic_atom.ml
	lib/syndic_common.ml
	lib/syndic_common.mli
	lib/syndic_rss1.ml
	lib/syndic_rss2.ml
Add namespace information for RSS 1.0 and Atom
Rename Invalid_namespace to Ignore_namespace
Multiple namespaces (see RSS 1.0 with namespace RDF)
Use List.mem instead List.exists and remove debug information
Merge pull request #24 from Cumulus/xml

Make Xml possible in the parse tree + misc improvements
Handle of namespace is more clear
Make the default namespace = "" (empty namespace)
Atom: check which tags/attributes need a namespace