Update and add more documentation

The unused `prepare_display` call is removed from existing files.  Following the list made in #190, documentation is added for:

- Geom.contour
- Guide.title
- Guide.colorkey
- Guide.xticks
- Guide.yticks
- Guide.xlabel
- Guide.ylabel

Rendered HTML files for `hg-pages` to follow once I get the Judo outputs to match the existing theme.