Refactored code for managing git object types.
Much refactoring and refinement of the YAML tags and
node graph filter code. Combined these into a
single stubbly.load function.
Move yaml2html into its own module. Factor out settings into
settings.py.
Rename stubbly.stubbly_loader -> stubbly.loader
Merge branch 'master' of https://github.com/Pitarou/htyaml

Conflicts:
	stubbly/node_graph_filter.py
	stubbly/yaml_tags/quote_as_strings.py
	stubbly/yaml_tags/stubbly.py
	stubbly/yaml_tags/test/test_yaml_tags.py

(I think the fork arose from an earlier screwed-up `git push`.
I really need to learn more about git.)