Use configured git author and author_email info

If the user has configured git on his system, we can fill-in the
author and author_email information with the values located in their
.gitconfig file.

The git commands to query for this information are:
- git config user.name
- git config user.email

This implementation will fall back on the current default text if the
git command isn't available.
Merge pull request #8 from epeterson/auto-fill-username

Use configured git author and author_email info