Wrapping up install script.

- This is rudimentary at best, but:
  - It will automatically symlink the root of the cloned repository to
    `/home/<username>/.vim`
  - It will automatically symlink the `vimrc.dist` provided to
    `/home/<username>/.vimrc`
  - It will gracefully exit on error.
  - It checks if `vim` and `git` are installed.
  - It sets scripts in `.bin/` to executable.