Added - Provide an example of gene lengths file in the `README.rst`
Fixed - Fix `fit` methods to match sklearn signature - Fix `LibrarySize` to always return `np.array` in private functions - Fix `get_norm_factors` to follow the `set_output` config - Remove leftovers of `as_frame` parameter
2.0.0
A mayor change (in fact, a total rewrite) comparing to `1.x`. API has completely changed to a `scikit-learn` compatible fashion and multiple new methods were added.