Updated code to run with Python3. Character case edits added to test_all_edit_ file.

[kaashish]

Changes:-

1. Updated the code to python3
2. Added changes to preserve edits where an annotator has marked sentence as grammatical.
3. Added an argument to reuse tokenized src,ref sentences.
4. Added changes to capture lower-case and upper-case edits. Updated m2 file: EACL_exp/m2converter/test_all_edit.ref.m2
5. Moved the test/ref files to specific folder.