Add support for Cool

Cool is the [Classroom Object-Oriented Language](https://en.wikipedia.org/wiki/Cool_%28programming_language%29), a language used in compilers courses at Stanford, Berkeley, UIUC, U.Va., Coursera, and elsewhere. Many of these projects show up [on GitHub](https://github.com/search?p=1&q=cool+compiler&ref=searchresults&type=Repositories), and given that the language is often used in class projects, there are likely far more private repositories containing Cool code than there are public ones.

This change includes a brief sample program I wrote to illustrate many of Cool's language constructs, as well as a simple rule to distinguish Cool files from Common Lisp or OpenCL (it has a line that starts with the word 'class'). Further, it includes a second example program adapted from an example contained in the Cool distribution (list.cl), which contains a few further language constructs and captures the style of a Cool program.