closes #27: initial commit on loading metadata

[yucongalicechen]

• Initial commit: Define vars(args) to load metadata into DO. wrote a basic test.
• I don't know if I overtest/undertest this. For example it seems that input_file, anode_type are both storing strings (or None), so it seems that it's enough to test one of these cases. Also, I need to test for True cases for force_overwrite. So I would say maybe instead of writing them all out, it's enough to test for string, float, and bool (3 arguments in total)?