Scprep

Changeset:
* upgraded `pandas` dependency from <0.24 to >0.25
* added `scprep.run.Slingshot`
* added `scprep.stats.differential_expression`
* added `scprep.measure.gene_variability` and `select.highly_variable_genes`
* added `scprep.io.download` submodule
* added `scprep.io.save_mtx`
* many bugfixes

Changeset:

* addition of `scprep.plot.colors`
* `plot.marker_plot` no longer fails with `NaN` input
* substantial refactor of `ScatterParams`
* various bugfixes

Changeset:
* added `scprep.run.splatter`, a Python port of the Bioconductor Splatter package
* added compatibility for Cellranger 3.0 10X files
* optional dependencies are now loaded at runtime
* `scprep.plot.marker_plot` now sorts markers and tissues by linkage by default
* bugfixes in multi-dataset histograms

Changeset:
* moved `scprep.hdf5` to `scprep.io.hdf5`
* added `scprep.plot.jitter`
* added experimental alternative to `fcsparser` for malformed fcs files
* changed `gene_set_expression` to not library size normalize by default
* `scprep.io.load_10X_zip` now accepts urls
* added examples to docs for scatter plots and jitter plots
* `scprep.plot.histogram`, `scprep.plot.plot_library_size` and `scprep.plot.plot_gene_set_expression` now accept multiple datasets
* various bugfixes and improved testing

Changeset:
* removed unmaintained MATLAB code, moved python code to root directory
* all subsetting and filtering functions now accept `extra_data`, which allows the user to filter multiple array-likes at once (e.g., library sizes, sample labels, other metadata)
* split out row and column selection functionality from `scprep.utils` to `scprep.select`
* renamed some functions in `scprep.filter` for consistency
* significant additional functionality in `scprep.plot.scatter`
* added `scprep.plot.marker_plot`
* minor bugfixes

Changeset:
* removed Python 2.7 compatibility in line with `matplotlib`
* added `plot` module ported from PHATE
* implemented random projections sparse input PCA
* bugfix knnDREMI
* temporarily enforce `pandas!=0.24.0` due to incompatibilities