Changed ProportionalWindow to use a tuple for input and output for simplicity
and used a namedtuple for output to keep the order top left bottom right
explicit.
Made the rectangle (top left bottom right) available to the module and
used it in TemplateFinder as well to make it more explicit and easier to use.
Moved _generic_proportions from one class to a module function since other
classes are going to be able to use it.
Moved corresponding generic_proportions test helper into the test module
for multiple tests to use.
Moved common module methods to their own test case. for now, just
_validate_proportions()
Minimized mocking, doing integration wherever possible.
Also standardized on using context managers to mock more precisely
rather than decorating the whole test.
Specified and implemented Grid.
added license note to readme
bugfix: proportions for cells were relative to each border rather
than relative to the origin of each cell. Fixed it by adding an internal
storage for the internal window borders.
Updated manual Grid confirmation (and therefore also updated readme using that code.