Woking solution

Hi. I don't know if you are still interested in this, but I made some commits to your js-clos project. This pull-req is just to let you know about it. 

The changes include:
+ Modify generics so that they can be called in a normal JS way
  + `foo(x, y, z)` instread of `CLOS.call('foo', x, y, z)`
+ Modify `defGeneric` and `defMethod` to cope with the above change
  + `defGeneric` returns a function object
  + `defMethod` takes the function object instead of its name
+ Added `defClass` with support for multiple inheritance
+ `defMethod` sorts the methods based on specificity
+ etc...

I made a gist to show the example use cases: https://gist.github.com/ympbyc/4996968

I apologize this is a huge commit. I hope this is worth reviewing.