Introduce 'giza http' command.

Resources are now broken when accessed via file:// as part of the protocol
agnosticism changes. You must now run 'giza http' and view the generated documentation
at localhost:8090 or whatever port you choose.
this is going to dump people out at ``build/`` which probably isn't right. 

maybe add some more options so that people can say: 

``giza http <builder/target>`` to see html/dirhtml/publish/etc. and have it default to "publish" 

also needs to consider:

- for sphinx_targets, if giza.content.helper.edition_check(c) then builder = builder + "-" + edition

- "publish" should `c.paths.public_site_output`.  which points to something "correct" in build/public/ where we stage builds locally before uploading them to production.