Episcanpy

- new QC plots and faster more memory efficient fct to bld ct mtx.

Major additions to this new release:
- TSS enrichment QC with epi.pp.tss_enrichment and epi.pl.tss_enrichment
- Latent Semantic Indexing available with epi.pp.tfidf, epi.pp.lsi
- In combination with the LSI we added epi.pp.correlation_component and epi.pp.filter_component to correct coverage discrepancy between cell barcodes.

Fix bld_mtx_bed function. Change default parameter of geneactivity function. Easier to load features (bed, gtf, gff files and macs2 peaks)

- no more api. Now --> import episcanpy as epi
- no more anndata2ri requirement
- update bld mtx functions
- update find genes and gene activity functions