Probably fix #2 introduced with ST 3014

It does not break functionality on my machine and @jbjornson
mentioned seeing it working somewhere.
Use the project's filepath as "hash"

The new code will work in both ST2 and ST3 and will try to migrate your project file history from using the old hash to the new project file name.

This is not quite perfect (in my mind) because there can be more than one workspace per project , and it would be nice to have a per-workspace history (rather than a per-project history).  Unfortunately there aren't yet any workspace related functions in the api.
(cherry picked from commit abfd579ed9654dcd1c3e44b0445feea80a82b47c)

Conflicts:
	file_history.py

Closes #4.