Similaritymeasures

- `curve_length_measure` is now vectorized which should improve performance. Thanks to a contribution by [nucccc](https://github.com/nucccc)

Changed
- `curve_length_measure` now supports curves with negative means! Thanks to a contribution by [Schmetzler](https://github.com/Schmetzler) in [PR37](https://github.com/cjekel/similarity_measures/pull/37)

Changed
- `area_between_two_curves` now correctly calculates the area of four points that form a triangle (where two of the four points are the same). Thanks to a contribution by [mcnick](https://github.com/mcnick) in [PR35](https://github.com/cjekel/similarity_measures/pull/35). Note that this change may result in different area values from previous versions. Cases where this will happen is if one curve had a perfectly straight line between three points, or if one curve had the exact same data point twice.

Changed

- `frechet_dist` now uses scipy cdist to calculate the distances between points
- `frechet_dist` should be significantly faster due to cdist thanks to a contribution by [nucccc](https://github.com/nucccc)

Changed
- `similaritymeasures.pcm` now produces different values! This was done to better follow the original algorithm. To get the same results from previous versions, set `norm_seg_length=True`. What this option does is scale each segment length by the maximum values of the curve (borrowed from the `curve_length_measure`). This scaling should not be needed with the PCM method because both curves are always scaled initially.
- Fix docstring documentation for returns in `similaritymeasures.dtw` and `similaritymeasures.curve_length_measure`

Added
- Added mean absolute error as `similaritymeasures.mae` thanks to a contribution by [HarshRaoD](https://github.com/HarshRaoD)
- Added mean squared error as `similaritymeasures.mse` thanks to a contribution by [HarshRaoD](https://github.com/HarshRaoD)