Added BFS and Greedy BFS in Lua

Hi,

I have included a new algorithm, a generic implementation of [Best-First Search](http://en.wikipedia.org/wiki/Best-first_search). This version also supports [Greedy Best-First Search](http://en.wikipedia.org/wiki/Best-first_search#Greedy_BFS), passing a boolean optional argument to the search function.
Tests have also been included, as well.

Regards,
Roland.