Create the Exporter super class and subclass it for Foundry

[tmcclintock]

The Exporter class should have the responsibility of taking the Dungeon object and the rendered image (from #3) and producing a serialized (i.e. saved to disk) file that can be ingested by an external program like Foundry VTT. This is the class that handles logic such as adding vision blocking structures (see #4) and any other information that we will be able to handle in the future.

exporter = FoundryVTTExporter()
file_path = "/some/path/to/blah.json"  # or whatever extension
exporter.export(file_path, dungeon, image)

For now we can use the dummy dungeon (from #3)

dungeon = [
    [1, 1, 1, 0, 1],
    [1, 1, 1, 0, 1],
    [1, 1, 1, 0, 0],
    [1, 1, 1, 0, 1],
    [1, 1, 1, 0, 1]
]

and it's rendering