Adds new command to list errors

I worked on adding a new command to list all errors in the file. This pull request has only small changes.

I also have more changes in this branch https://github.com/Osso/SublimePythonIDE
Our team is using it but it needs to be cleaned up before merging.
So I am asking before I do the work, if you are interested in merging the pylint integration or not.