New 3rd-party dependency: cl-yaml

I have an application where I want to load yaml files into lisp. After some search, I found this library which wraps around a c-library which is in the debs. It does not require any further external common lisp dependencies.

cl-yaml offers yaml 1.1 support through libyaml (the c lib), while ROS itself is using yamlcpp which supports yaml 1.2. So, this is behind the curve.

Compilation worked fine for me (Ubuntu 12.04, ROS Hydro). However, the original asd (see below) still invokes the c-compiler to build some wrapping code. I still need to rosify this. So, please do not merge this just yet.

I opened this pull request to get feedback about this lib. Fire away on comments, objections, ideas for improvement.