Added Rabin_Karp in Lua

Hi,

Added [Rabin Karp](http://en.wikipedia.org/wiki/Rabin%E2%80%93Karp_string_search_algorithm) string searching algorithm implementation in Lua, with tests.
Note: I also refactored the [test file](https://github.com/kennyledet/Algorithm-Implementations/blob/master/Knuth_Morris_Pratt/Lua/Yonaba/kmp_test.lua) for the Knuth-Morris-Pratt Lua implementation.

Regards,
Roland.