add sparks.utils, a collection of mini-function relatively non-sortable but well, useful.
Ability to return only letters for unique_hash(). It's probably less unique, but this works and we don't need a math-perfect implementation.
bump version in setup.py
Merge branch 'release/1.13.7'
Merge tag 'sparks-1.13.7' into develop

1.13.7