Repeating bigrams handled incorrectly

[stagha]

This can be demonstrated by the below code snippet:

var testString = "aaaaaaaaa";

var diceCoefficient = testString.DiceCoefficient(testString);

Assert.Equal(1, diceCoefficient);

The test fails. The reason is Intersect returns the distinct overlapping bigrams. But you then divide by the number of bigrams in the two strings including duplicates, which is incorrect.

https://github.com/tylerjensen/FuzzyStrings/blob/master/src/DuoVia.FuzzyStrings/DuoVia.FuzzyStrings/DiceCoefficientExtensions.cs#L36