The 'manual fixups' are:
- incorrect use of dict.items() where dict.iteritems() was meant; this
results in list(dict.items()), which I changed to dict.items().
- removal of 'from __future__ import' lines, which 2to3 changes into
empty lines; I removed the empty lines.
- Comments are stored in HTML as well as Markdown, so that conversion
only happens when saving (rather than when viewing).
- Added 'markdown' Jinja filter for easy development. This is quite
a heavy filter, so it shouldn't be used (much) in production.
- Added CLI command to update schemas on existing node types.
