add init error in panel if SublimErl cannot be initialized
Better project directory and source file tests

The current tests fail if a user stores *all* their source code in a
~/src directory

Test for ebin because it's required by the rebar layout, and is more
erlang specific.

Test for exclusion of .eunit. Not sure if there are other .erl files
we'd want to ignore.
bump version to 0.5.1