Add CHEMBL.TARGET ID Mapping

[kevinxin90]

Add CHEMBL.TARGET as a xref field for MyGene.info.

{
"chembl_target": "CHEMBL1223344"
}

[kevinxin90]

If it can not be resolved, let’s just skip it. If multiple CHEMBL IDs mapped to the same Gene, this field should be a list.

[newgene]

CHEMBL Target ID mapping to Uniprot IDs can be obtained from:

https://www.ebi.ac.uk/chembl/g/#browse/targets
(Download as a CSV or TSV file for all 15K targets)