Pyranges

- support for multiple (repeating) attributes in gtf reading
- fix handling of kwargs in apply, apply_pair, apply_chunks
- add to_example(nrows=10) to get a copy-paste friendly representation of a PyRanges
- add pr.from_dict() to create a PyRanges from a dict (like the ones produced with to_example)

- fix small bug in jaccard
- remove leftover debug-print in pr.random()
- add experimental gr.stats.forbes
- fix handling of kwargs in apply, apply_pair, apply_chunks

- random also takes dict as chromsizes argument (like {"chr1": 249, "chr2": 242})
- fix reldist bug when grs have different chromosomes

- fix various issues with reading and writing gtf/gff3 (1-indexing, removed final ";" in gff3 attribute col when writing)
- remove ModuleNotFoundException in __init__.py (3.5 < only)
- gr.overlap(gr2) now has default argument how="first", i.e. only return overlapping intervals once, even though there are multiple overlapping features in gr
- fix bug in pr.stats.mcc when using stranded data

- add Simes method to pr.stats
- add keys argument to pr.iter
- make strand=None default arg for concat
- gr.split() does opposite of merge
- pr.count_overlaps(grs, features=None) like bedtools multiintersect added
- set mkl.set_num_threads to 1 in __init__

- add value col argument to to_bigwig (thanks https://github.com/liyao001)