Relented on the strict import of direct objects/classes for the typing
module only. Typing module components can be directly imported because
it makes the code really painful to read and write otherwise.
This is still in-line with the python style guide adopted from Google at
http://google.github.io/styleguide/pyguide.html section 2.2.
At the moment these are no different than strings, but they allow us to
do things like add URI handlers to file names if no scheme is provided,
and eventually do file existence testing. This also allows the web URI
to allow uploads as a means of passing a file in.
The configuration will only store the filename, because otherwise
someone could add a huge file which would need to be carried around in
the config forever after. Handling file existence errors is up to the
UI after the volatility library returns a "file not found" type
exception.
Mike Auty