Add support for .gitattributes files/templates

[ajmwagar]

Reddit user /u/maiteko, mentioned it would be nice to have a similar tool to bliss for .gitattributes.

Why not just build in support directly?

Feel free to comment on what features are desirable.

Current features planned:

• [ ] Support .gitattributes template files
• [ ] Support caching for .gitattrubutes