Allow ignore=pattern definitions in .wakatime.conf to ignore files

Wakatime is forever reporting my emails as /tmp/mutt-blahblahblah and I personally don't care to be reminded how many and what number of emails I had to send so I added this to let me include ignore patterns in the config file (e.g. `ignore=/tmp/mutt-.*`).

As mentioned in the TODO comment the config parsing code is duplicated and should probably be merged into a single one but I didn't have time to do that yet and it seemed like a separate issue.