Custom source path

Added support for custom source path under the `src` and `test` directory. It fixes inserting/updating the namespace and switching between test and implementation if the project has a different source layout (e.g. sources in `src/clojure` and tests in `test/clojure`). 

I'm a complete noob with elisp and I hope it's ok. I'm not even sure how to write tests for it :(

Haim