Function ratio 

pub fn ratio(s1: &str, s2: &str) -> f64

Calculate how similar two strings are, as a score from 0.0 to 1.0.

A score of 1.0 means the strings are identical, and 0.0 means they have no character in common. In between, the score is the share of characters the two strings have in common, known as the indel similarity ratio:

ratio(s1, s2) = 2 · LCS(s1, s2) / (|s1| + |s2|)

where LCS is the length of the longest common subsequence and |s| is the number of characters in s. Two empty strings score 1.0.

Examples

assert_eq!(lev::ratio("kitten", "sitting"), 0.6153846153846154);
assert_eq!(lev::ratio("abc", "xyz"), 0.0);
assert_eq!(lev::ratio("", ""), 1.0);
assert_eq!(lev::ratio("résumé", "resume"), 0.6666666666666667);