STAR index wrapper with GFF

[andreott]

Is your feature request related to a problem? Please describe.
When using STAR index with a GFF instead of GTF file, the flag --sjdbGTFtagExonParentTranscript Parent needs to be passed.

Describe the solution you'd like
Obviously the user can provide the appropriate argument as extra. I just want to explore whether you would consider to integrate this logic into the wrapper - checking for file extension and in case of gff(3), add the flag. Or maybe another named parameter like annot_format which then translates into the command line argument.

If you like the idea, I can also provide a PR.

[fgvieira]

Sounds good! Just make a PR and I'll look into it.