Provide option for expecting dynamic context to be just a module

[mwchase]

I kind of want to support ward, and right now, the easiest way to handle that is some kind of plugin that only reports the test module path, which would need to be handled somehow.

Alternatively, there could be a plugin that handles ward's "module:line number test description" format, and pytest's "module::test name" format.

I'll need to look into writing plugins against various things in order to know how best to handle this.