Djblets gained support for a better way of specifying types for fields

and request parameters in the API. This moves us over to these new

types, fixing up the documentation generator in the process to ensure

we're still generating documentation correctly.
In almost all cases, we're using the modern equivalent of the legacy

field types. However, fields for date/time strings have been updated to

use DateTimeField, which will generate nicer documentation by default

(removing the need for us to specify time formats) and will handle

validation for us (removing the need for us to parse the strings).

Unit tests pass.
Built the docs and compared the generated HTML output to the output

using older field types. Except for some slight differences in how we're

representing things now, the output was the same.