Added Prima::Drawable::Record, including a basic test suite.

It will now be much easier to test drawing operations onto a canvas.
I need to document it, sooner rather than later, but not yet.
Added Test::Prima with basic docs and tests
Have a working Subcanvas test (though the test still fails)
Added is_prima_image to Test::Prima
Rewrote subcanvas test to use is_prima_image
Made color test failures due to non-integer colors a bit clearer
Updated Test::Prima tests for change in diagnostic output
Wrote some tests to confirm (and in some cases refute) my Prima knowledge
Further explored my understanding of Prima's translate and clipRect behavior with t/21_Subcanvas.t
Finally got Subcanvas working!!
Added comment in Talk docs about custom footer fields