Prefer RCRC environment variable over ~/.rcrc

* Centralize configuration loading in rcm.sh(.in)
* Check for readability, not just existence

Add RCRC notes to all manpages. Putting the environment variables in a
table lines them up more neatly and definitively, across all output
formats, and also follows the examples used by e.g. BSD ls(1).
Unset the CDPATH before running the program

As reported in #23, you can trick `rcup` into installing into `.` with
this `CDPATH`:

    export CDPATH=/tmp:.

As described [online][1], it is a mistake to export the `CDPATH`
environment variable to begin with. Since it is a one-liner to work
around it, though, it's worth fixing.

The workaround is to unset `CDPATH` at the beginning of the script. This
does not affect the outside environment, it only affects the script and
its functions.

[1]: http://bosker.wordpress.com/2012/02/12/bash-scripters-beware-of-the-cdpath/
Fixed typo in rcm manpage
Rename the homebrew repo.

Having a single homebrew tap for all of thoughtbot's projects makes sense.
Update the NEWS
Fix NEWS format, fix typo

* The NEWS format was off: bullets must be preceded by two spaces.

* The word 'committing' was misspelled; hats off to debbuild's linter
  for catching this.
Bump to 1.2.0.
Fixed typo

Someone had dots on the brain
Allow {pre,post}-up hook directories

If the `pre-up` or `post-up` files are actually directories, run the
executable contents of them in an arbitrary order.
Force some directories to be symlinks

Typically a directory structure is copied instead of symlinked, while
files are symlinked. However, some cases require symlinked dirs: git
submodules, vim plugins, and so on.

This introduces a `SYMLINK_DIRS` option for rcrc(5) that takes a
space-separated list of "exclude patterns". Any directory matching these
patterns is symlinked.

This also introduces a `-S` argument for lsrc(1), rcup(1), and rcdn(1).
This argument takes a pattern, for one-off directory symlinking. It can
be repeated.

This also introduces `-S` and `-s` for mkrc(1). `-S` will re-install the
files as symlinks, and `-s` will not.

This does work with `-C`, though perhaps unintuitively - we don't know
what the user means in this case. However, it will not crash.

Bug: `-s` does not work right if `SYMLINK_DIRS` is set. Bug #36
addresses this.
Use sed to split out the short hostname

Instead of using the non-standard `-s` argument to `hostname`, use `sed`
to split out everything after the first period. This fixes lsrc(1) on
Cygwin, among others.

Fixes #28.
Fix error when hooks files/dirs don't exist

We had been relying on `hooks/pre-up` and `hooks/post-up` files to
exist. This explicitly checks first.

Fixes #34.
Add sigil (`$`) for symlinked dir for lsrc -F

The `$` sigil in `-F` indicates that the directory is symlinked instead
of recurred upon.

Fixes #37.
Add install instruction on Gentoo-based systems

Add instruction how to install rcm on a Gentoo-based GNU/Linux
distribution. Currently the overlay is maintained by Anton Ilin
(bronislav).
Start bringing in the Makefile.am from gitsh

It introduces the `Makefile.am` from gitsh, and abstracts it a bit. This
`Makefile.am`, or most of it, could be dropped into gitsh again. How to
use it is documented in `DEVELOPERS.md`.

The whole release process is more consistent and simple: `make release`
to build a tarball, Homebrew, Arch, Debian, HTML (from manpages), and
tag it, pushed to the various repos, and with cleanup. The `release`
target is composed of smaller targets that stack well.