[BUGFIX] Monthly vs yearly

[bkj]

Add support for yearly projections.

cc @ezekielbarnett

[bkj]

This should be fixed in 0.2.2

[bkj]

[BUG] Treating seasonality "period" as "period" time steps (years or months) rather than "period" months. Probably should just disable seasonality entirely for yearly data, since it doesn't make sense to have 12-month seasonality at 12-month sampling resolution.