Satsuki

**Summary**:

* (ENHANCEMENT) Code clean up.
* (ENHANCEMENT) Add pylint, flake8 to CI.
* (ENHANCEMENT) Revamp Travis CI to test Windows, Mac, Linux.

**Summary**:

* (ENHANCEMENT) Updated for compatibility with GravityBee's new directory structure (using ``.gravitybee`` directory).

**Summary**:

* (ENHANCEMENT) Code clean up.
* (ENHANCEMENT) Changed SHA default to None.
* (FIX) Fixed bug in tests affecting SHA hash test.

**Summary**:

* (ENHANCEMENT) Tag can now be based on info file written by GravityBee (app version from).
* (ENHANCEMENT) Allow sha256 hashes to be added to label or uploaded as a separate file.
* (ENHANCEMENT) Improved testing of SHA hash (downloading file and recalculating.
* (ENHANCEMENT) Added ability to recreate releases in order to update the tag/commitish associated with the release. Otherwise,releases can be updated but will always point to the same tag/commitish.
* (FIX) Fixed various bugs with SHA hashes, creating releases, deleting tags, and revamped upload error handling.

**Summary**:

* (FIX) Many bug fixes improving compatibility with Windows.
* (ENHANCEMENT) Use new GravityBee file (``gravitybee-files.json``).

**Summary**:

* (FIX) Implemented file (release asset) delete
* (ENHANCEMENT) Generally improved asset handling including SHA256 sums for files and better error handling