adds --parallel-options option to parallel_stereo

[AndrewAnnex]

adds gnu parallel options pass-through for parallel_stereo

Description

adds a argparse param to parallel_stereo that accepts a string input of additional parameters for gnu parallel, currently not parsed/validated in any way as we assume gnu_parallel will handle the errors.

Related Issue

fixes #335

Motivation and Context

allows passing in flags such as sshdelay to gnuparallel to work within bounds of hpc clusters

How Has This Been Tested?

not tested

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.

Licensing:

This project is released under the LICENSE.

• I dedicate any and all copyright interest in my contributions in this pull request to the public domain. I make this dedication for the benefit of the public at large and to the detriment of my heirs and successors. I intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this contribution under copyright law.

[AndrewAnnex]

note, the call to split(' ') may not actually be needed at all, I just decided to have it for now to be consistent with the cmd list variable

[oleg-alexandrov]

Andrew, thank you!

I tweaked a bit the doc, while hopefully reflecting your original intent.