Added a custom delimiter field for the Ignore Committers field

[MarcAtPlumbee]

There was an earlier pull request that wanted to replace the space delimiter with a comma delimiter. That pull request was denied due to lack of backwards compatibility. This pull request maintains the default space delimiter for backwards compatibility and adds the option to choose a custom delimiter.

[dwilson6]

I would like this feature as well. Having spaces in a username is not that unusual.