added option where to branch from (if different than the default branch)

[FitzgeraldKrudde]

I implemented specifying where to branch from.
Useful when you want to branch from a different branch than the default branch.

I tested the change and verified the resulting PR in the Azure GUI. This looked OK to me.

Please review/QA/merge.

Also see: #49

[operte]

I left a couple of comments.

azdo allows picking the source and target branches. This PR assumes that these are always the same. I have two main questions:

• If we want to continue with this approach, I think we should pick a better option name.
• We could also allow the user to specify source and target branches separately, following the azdo cli more closely.

Not sure what the best option is. Let me know.

[FitzgeraldKrudde]

Our usecase is that we want to branch from (and to) a different branch than master, for example develop.
I.e. source and target branch name are intentionally combined.

I would prefer than a better named parameter as opposed to using 2 parameters.
I think starting-branch sounds like a good name then.

Is this OK?

[operte]

Yes, I see. I also believe it's not common to branch from one branch to a different one.

I thought a bit more about it and I'm even less happy with the other names, so let's keep default-branch. But let's change the docs a bit. I'll update my comments.

[operte]

Can you think of any unit tests that we could add to the project?

[FitzgeraldKrudde]

I am a bit of a python newbie.. I am not familiar with python unit testing

[operte]

Thanks! :)