Add Ruby version of the Yahtzee kata.

Signed-off-by: Lennart Fridén <lennart@devl.se>
Revert undesired changes to the README.

Signed-off-by: Lennart Fridén <lennart@devl.se>
Merge pull request #16 from DevL/add_ruby_yahtzee

Add Ruby version of the Yahtzee kata.