Add support to index names for gff tabix (#780)

[billzt]

Modified according to the functions of vcf names indexing. Aim to fix the fourth bug in #780

[cmdcolin]

this is great! does this only index the ID of the features? it could be useful to index other fields, possibly at the user's command

[billzt]

Yeah, this would be a little more complicated than vcf. Perhaps adding a novel parameter to generate-names.pl is more robust. However I'm not sure whether it is acceptable.

[cmdcolin]

at least one thing that is sort of interesting is that with normal flatfile-to-json.pl on a gff file, you use the --nameAttributes parameter of flatfile-to-json.pl to determine what parameters of the gff you want to have indexed by generate-names.pl

so, potentially if the gff3tabix was incorporated into flatfile-to-json.pl then it might hook into that parameter

[nathanhaigh]

Would this work for GFF3 files on remote storage? e.g. the baseUrl is an http address.

[rbuels]

@billzt sorry about the delay here. Would you be willing to add a test case for this to the automated tests in `tests/perl_tests/generate-names.pl.t?

[billzt]

@rbuels Sorry, I didn't know how to add the test ...