Include notes for the previous two releases and the current release in
progress.

Wasn't thinking about the fact that these helper functions get exposed
to the global namespace, which is _such_ a bad idea.

Rename these functions to something specific to the program to make them
harder to randomly come across and to have a better chance of not
overriding something that already exists.

* Enable installation via Homebrew on OS X.
* Update the README to describe how to use Homebrew to install.

This was our ideas file when implementing the new database supported
version of `qcd`. Now that it's working the way we wanted it to, this
ideas file can be removed.

Include a short description, example usage information, installation
instructions, and license information.

* COPYING file
* Copyright headers on source files

Assume we'll get these from the main `qcd` script as currently they're
sourced to the global environment. This way at least we're not repeating
those lines in two places.

Bash completion now works for the new database-backed `qcd`.

Arguments 1 and 2 are completed by searching the `qcd` database.
Argument 3 is completed using default Bash completion by setting
`COMPREPLY` to `()` and adding `-o default` to the `complete` call as
recommended here:

http://stackoverflow.com/questions/12933362/getting-compgen-to-include-slashes-on-directories-when-looking-for-files/19062943#19062943

Copied over the directory variables from the `qcd` script. Not sure if I
should be putting them somewhere else so they're not in two different
places. I probably should. I was also concerned that once the scripts
are sourced, these variables will be in a user's shell environment. That
doesn't feel right, but I'm going to ignore it for now.

In addition to creating the config directory, also touch the database
file to ensure it exists before we query it with `awk` in
`shortcut_exists`.

Add a comment describing what those seemingly random slashes are for.