Check first for existing branches before creating them

[wrandall22]

This PR is another attempt at fixing issue #10 after the reversion in #12. I found the echo lines to be helpful, but we can delete them if desired.

[wrandall22]

This needs more work still, unfortunately, GetBranch fails with an exception instead of returning an empty object when the branch does not exist, so this needs some error handling.

[wrandall22]

I believe this is working now (tested on a non-existing and existing branch). However, there is a side effect of a log in the console: sh: "branch":: unknown operand that shows up when the branch does exist.