Difference between documentation and implementation for SMAPE

Hello, everyone I was reviewing the SMAPE for v2.0 and I found something odd that may be a mistake in the documentation or a misunderstanding on my end. The [documentation](https://permetrics.readthedocs.io/en/v2.0.0/pages/regression/SMAPE.html) use the formula that includes the 2 in the numerator, which, according to [this wikipedia page](https://en.wikipedia.org/wiki/Symmetric_mean_absolute_percentage_error) (that is linked into the docs), means that the SMAPE will range between 0 and 2 (or 0% and 200%). However, the docs specify that the SMAPE will range between 0 and 1, which is not totally wrong, because in the implementation ([see here](https://github.com/thieu1995/permetrics/blob/v2.0.0/permetrics/regression.py#L357)) one can see that the 2 is missing and as such, the SMAPE, as calculated by the library, will range between 0 and 1. The issue here is that the docs shows one formula (the one whose results range 0 and 2) and implements the other one (the one whose results range between 0 and 1), which is a bit inconsistent. Maybe dropping the 2 from the formula will be the easiest solution, although it would be nice to be able to parametrize and have both metrics.