Debian packaging

[regularfry]

This set of patches adds a very basic debian package definition. The package installs to /usr rather than /usr/local, and puts the documentation in the right place.

There are a couple of minor tweaks to the Makefile necessary to get this to be smooth: firstly, the debian helper scripts expect the Makefile to respect the DESTDIR environment variable, which I've added. Secondly, the helper scripts install the docs themselves, and don't rely on the make install task to do it for them. This means that before I split the make install task out to make install_files, I was getting two sets of documents installed, which was a little untidy.

The package installs and works on Debian Wheezy. I haven't tried it on an Ubuntu, but I think it should work without modification.

[postmodern]

Spoke with someone more knowledgeable of Debian Packaging. It shouldn't be necessary to split the install task. It's ok if dh_installdocs re-installs any documentation. DESTDIR stuff looks good.

[regularfry]

Sorry, I'm not sure I understand. dh_installdocs installs the documentation to /usr/share/doc/chruby/, which is the "right" place according to Debian. make install installs them to /usr/share/doc/chruby-0.3.6/. If I disable dh_installdocs, I only get docs in the wrong place, and if I don't, I get both sets.

Would it be better to let Makefile's DOC_DIR get overridden by an environment variable to put them in Debian's preferred location?

[postmodern]

Ah ha. It looks like I used the RedHat style of DOC_DIR (name-version). Yeah, let's make DOC_DIR configurable and default it to PREFIX/share/doc/NAME.

[jnv]

Bump; is there anything particular that prevents this PR from being merged?

[postmodern]

@jnv I believe just ensuring documentation is installed in the correct location. That and rebasing it against current master.