Previously, we were using the "statistical", technically accurate name. Instead, we
should probably use the name that people are familiar with, e.g. "Holt Winters" instead
of "triple exponential". To that end:
- `single_exp` becomes `ewma` (exponentially weighted moving average)
- `double_exp` becomes `holt`
When the `triple_exp` is added, it will be called `holt_winters`.
Colin Goodheart-Smithe
Zachary Tong
Pascal Borreli