BUG: Restore support for passing tuple of colors to Strategy.I

Broken since kernc@bae9340

MNT: Install dependency pre-releases on CI

REF: minimal unrelated changes

BUG: Fix plot saving to filename regression since ab0cbe5

The plot would save to filename even when run in notebook. Argh.

Refs: kernc#45

MNT: Travis CI, bump default Python to 3.8

ENH: Make plot span 100% of browser width by default

MNT: Fix setup.py warning

DOC: Fixed documentation

Some minor documentation fixes.