Solves the Entropy challenge
Added a solution for the Fibonnaci word problem
Made the shannon_entropy() method public for reuse, and upgraded precision to f64
Update README.md

Added the description of the new tasks done.
Update entropy.rs

Added back-link to rosetta code
Update fibonacci_word.rs

Added back-link to rosetta code
Merge pull request #2 from TisButMe/master

New solutions