End-user and contributor documentation

[idpaterson]

The new workflow attempts to be fairly self-explanatory, but there will be some documentation needed. Most importantly so far, #53 will probably require the user to install PyICU in order to support localized date formats. It may be possible to provide an option in the Preferences menu to install that, but perhaps not if there is a lot of console interaction involved.

Landing pages will also be needed for post-authentication to welcome the user and provide a brief intro to the workflow. An index page will be needed for the gh-pages documentation since throwing users directly into Python code docs might not be the most helpful thing to do for non-contributors.

The documentation for the current version will be located at ./docs with a submodule referencing the repository's gh-pages branch at ./dist/docs. This allows contributors to have a prebuilt copy of the documentation for the current version without forcing an update to gh-pages until release. Jekyll will probably be useful for handling the combination of how-to pages and source documentation that I need.

[idpaterson]

GitHub now supports hosting the repository's pages from a docs/ directory in the master branch. This will be much more maintainable than the submodule approach discussed above.