PKGBUILD-git improvements

- Remove two configure flags which just caused warnings.
- Replace `pkgver` function with a working one.
- Explicititly `cd` into `srcdir` before `gitname` as found in
  `PKGBUILD-git.proto`.
- Bump `pkgrel`.
- Specify correct package version.
Allow the user to override SYMLINK_DIRS with -s

This adds a `-s` that can be used to override the `SYMLINK_DIRS` config,
or the `-S` flag, to lsrc(1), mkrc(1), rcup(1), and rcdn(1).

The `-s` flag is the opposite of -S: any argument, if it is a directory,
is not symlinked but instead recurred down.
rcdn(1) -K -k

The rcdn(1) program is all set up to handle the `-K` and `-k` flags,
except those flags were never actually allowed through `getopts`.

Thanks to Mikkel Fahnøe Jørgensen for discovering this.

Closes #93.
Fix -I in rcdn(1)

The prior fix for `-k` moved the `:` from after `I` to after `k`. Move
it back.
Installation instructions for Ubuntu

Add instructions for how to install rcm on Ubuntu using the
[~martin-frost/thoughtbot-rcm
PPA](https://launchpad.net/~martin-frost/+archive/ubuntu/thoughtbot-rcm)