Integrate `join` sub-command to join multiple GFF files

The main function that does this is already coded here:

https://github.com/miRTop/mirtop/blob/dev/mirtop/gff/merge.py#L3

dts is a dict where keys are sample name that could be the basename of the GFF file that are the input to the command, and values is nested dicts with the following structure:

dicts['colum0']['column4'] = [list1, list2, listn]

Each listn contains 4 elements: [IDU,NA,EXPRESSION, GFF_LINE]

Each value represent a variable inside attribute column as explained here:https://github.com/miRTop/incubator/blob/master/format/definition.md , except for the last one that is the entire GFF line.

Noted NA could be an empty value, that is not needed for this specific functionality.

Basically, it's needed a function to read each GFF to have the structure above explained, and the input that to the function merge.

Header needsto me modify to add the:

CMD info that has the command line used
COLDATA info needs to be outdated with all the sample names

If this is unclear, just think a way to join two GFF, for instance from: https://github.com/miRTop/mirtop/blob/dev/data/examples/gff/correct_file.gff

Final function need to be tested and added as a unit test in https://github.com/miRTop/mirtop/blob/dev/test/test_functions.py

Thanks

miRTop / mirtop

Integrate `join` sub-command to join multiple GFF files #31