Add test harness for stowrc files

Why:

* Planning on developing a new feature for parsing of stowrc files.
* Need a test harness that performs initialization and clean up
    * Initialization: Create directory structure that allows creation of
      stowrc files without worrying about squashing existing files.
    * Clean up: Remove all files created during testing.

This change addresses the need by:

* Add intialization and cleanup harness in t/rc_options.t
    * Define the location to write stowrc files to in $RC_FILE
    * Ensures that location $RC_FILE does not already exist.
    * Calls the init_test_dirs to bootstrap directory tree.
    * After all tests are run, removes $RC_FILE and the testing
      directory tree.

* Add basic test of stowrc parsing to t/rc_options.t
    * Provides a template of how to create and test a stowrc file.

* Newly created t/rc_options.t file added to MANIFEST

MANIFEST

@@ -45,6 +45,7 @@ t/ignore.t
 t/join_paths.t
 t/parent.t
 t/stow.t
+t/rc_options.t
 t/testutil.pm
 t/unstow.t
 t/unstow_orig.t