A custom plugin that invokes a system copy to OS X's pasteboard using
`pbcopy` via a Vim command. This allows us to specify a range of lines
to copy in command mode, similar to the way that Chris Toomey's System
Copy plugin provides an easy way to invoke a system copy using motions.

With this plugin we can write:

    :5,21Copy

to copy those lines.

    :12,'aCopy

will also work.

If your Vim is compiled with `+clipboard` support, you would instead
write:

    :15,24y *

Since I use a Vim that doesn't have clipboard support, I decided to use
a plugin to get the same functionality rather than compile a new Vim.