Multiple small improvements:

 * Added optional configuration file, trac2github.cfg
 * Milestone can now be empty
 * Information about original reporter/author/time added to the issue text

The configuration file was really only added to make it simpler to update the script code and then check it in. If the configuration is in the same file I have to undo the configuration before committing.

The information added to the top of each issue/comment looks like:
**Reported by sm0svx on 2014-06-29 20:30 UTC**
An example of how it might look in reality can be seen [here](https://github.com/sm0svx/svxlink/issues/22).