Added Move To Front transformation

Hi,

[MTF](http://en.wikipedia.org/wiki/Move-to-front_transform) (Move-To-Front) Transform is a transformation algorithm that encodes a stream input, so that running a compression algorithm later on this transformation would enhance its compression rate.
Find in this PR a simple Lua implementation of this algorithm, with tests.
Since it is a new algorithm, I have added appropriate tags.

Regards,
Roland.