added some YARD & converted cmd_load*, alias plugin

- added a bunch of YARD documentation, but needs more
- cmd_load converted to normalized approach
- converted loadpath's tab completion to tab_complete_filenames_no
readline
- the above method was added to dispatcher_shell
- added get_all_commands to dispatcher shell
- search -c uses the above method
- search -s can be completed easily, not done yet
- tab_complete_by_words_length is probably needlessly complex & likely
will be removed
- alias plugin fixed an unlikely to be important bug
- alias plugin now calls get_all_commands too