[wd] New minor version (v0.4)

Added features:
 * Added test suite, using `shunit2`
 * `show` command now takes an optional warp point as argument, showing its path
 * `clean` removes all warp points to non-existent directories (use `clean!` to force)
 * `--version` to print version
 * `--quiet` to silence all output
 * `--debug` to exit with return codes (for debugging/testing)
 * `--config` to specify config file (for debugging/testing)