Restrict list of scanned directories 

The patch improves performance by introducing new config option `:paths`. New option restricts the set of scanned directories.

Our Leiningen project has around  ~10k files.Only 200k are relevant for tasks executed with auto. Restricting directories to source and test reduced CPU consumption from 80% to 1%.

By default `:paths` is set to concatenation of project `:source-paths`, `:test-paths` and `:java-source-paths`.