Grave accent

[PicusZeus]

I needed a functionality that allows to change accent in oxytones to grave (or to add it, if there is no accent), and that checks if a word has such an accent, so I added them to your code. I called the new function in the accentuation module make_varia. You can check the code on my fork of greek-accentuation and maybe add it to the library.

[jtauber]

Great thanks! You can do a pull-request if you like (but don't include any other changes or version bump).