Create Slice Syntax for tied_list for make_tied_positions_dict.py

[zhoubay]

Hi there,

In my using senario, PDB structures are often not exactly homolog, while they share lots of same amino acids. Therefore, if the make_tied_positions_dict.py supports some kind of slice syntax instead of typing all homo amino acids in one string, that would be much more helpful in my opinion.

Thus, I made a little amendment to make_tied_positions_dict.py, adding a function to support slice syntax. Example Bash and Parser help were added or changed, too, to support that.

Please check and Merge! :)

Thank you for checking this!

[Germanki]

This would be really helpful! I'd definitely appreciate this being added to the code.
Would you also be able to make this work for make_fixed_positions_dict.py?