chainladder 0.8.9

Enhancements

• #198 Added projection_period to all Tail estimators. This allows for analyzing run-off beyond a one year time horizon.
• #214 A refreshed docs theme using jupyter-book!
• #200 Added more flexibility to TailCurve.fit_period to allow boolean lists - similar to Development.drop_high
• @kennethshsu further improved tutorials

Bug Fixes

• #210 Fixed regression in triangle instantiation where grain=='S' is being interpreted as seconds and not semesters.
• #213 Fixed an unintended Triangle mutation when reassigning columns on a sparse backend.
• #221 Fixed origin/development broadcasting issue that was causing silent bugs in calculations on malformed triangles.