Add tooling to allow for user-defined post question pick command

[john-d-murphy]

For CPP files, I found that I needed an extra file in my code folder to prevent my editor's code anaylsis from throwing spurious warnings.
It makes sense to copy this file into the code folder after every pick action, and it also makes sense to not have this hard-coded since other people's dev environments may be different.
Therefore, this PR allows a user to set thier own default action to take after a pick action has been completed.

I'm happy to make any edits to this or to have this thrown out - it's my first bit of Go code and I'm not sure if this even warrants a feature request.

For context, I'm using this to push build commands and a test framework to each problem so I can do a build and test on a given problem's tests in vim directly.

[j178]

Thanks for your PR! I’m unavailable to review it at the moment, but I’ll get back to it in about a week. Thanks for your patience!

[john-d-murphy]

Thanks for your PR! I’m unavailable to review it at the moment, but I’ll get back to it in about a week. Thanks for your patience!

No problem! Whenever you're ready. I realized I needed to write the code for my use case, and I figured I'd share. Absolutely no rush, and I'm happy to describe how/why I'm using it when you're ready.