v0.2.0

Improved pipeline: added mtx.gz as allowed input format for read count matrix and removed unneeded 'dmeta' and 'meta' files.
Added commands airqtl utils convert_anndata and airqtl utils convert_vcf to convert anndata and vcf files to input format for airqtl.
Improved AIR class in operator handling, pytorch interface, and tests.
Bug corrections.
Improved tutorial, documentation and logging.