[ENH] Improve `get_chromosomes_from_ensebml` code and logic

[fraimondo]

In get_chromosomes_from_ensebml

hipsnp/hipsnp/hipsnp.py

Line 634 in 76963bf

def get_chromosomes_from_ensembl(rsids):

Problem:
We currently do one request per RSID and parse the json in a not-so-good way.

We can improve this method by:

1- Using a combined request to ensembl.org REST API.
2- Checking the json response properly.

Todo:

• Replace the GET request for each RSID to variation/human/ (https://rest.ensembl.org/documentation/info/variation_id) for a POST request to (https://rest.ensembl.org/documentation/info/variation_post)
• Parse the json file and check properly the mappings list. We need to decide what to do if we find more than one. Currently, we just take the first.