Cache blame results with a project-specific filename instead of always using blame.json

[thehale]

It would be nice to support caching blame results for multiple projects at the same time so that blame doesn't have to be recomputed every time a user switches projects.

This could be accomplished by changing the naming format of the cached blame file to include project specific information. When that project information changes, a new cached blame file will be created/read as appropriate.

The proposed naming format is

OWNER-PROJECT-COMMIT_HASH.json

For example, the current tip of this project would have a cache file of

thehale-git-authorship-1e244fd8fb4efdec68a598fdf1154c48909e76b9.json

This format will cache blame files for a specific commit in a specific project.

[thehale]

An alternate approach that would also be welcome is a subfolder approach:

./cache/OWNER/PROJECT/COMMIT_HASH.json