Replace DiceCoefficient implementation

I've been using it for almost a year now, and in my benchmarks it performs much better than original implementation (at least for shorter strings, I'm limited to <2048 characters). And as pointed out in tylerjensen#8, current implementation may produce incorrect score for repeating bigrams.

The downside is that this is O(n*m) implementation and will perform much worse on long strings.

Fixes tylerjensen#8

src/DuoVia.FuzzyStrings/DuoVia.FuzzyStrings/DiceCoefficientExtensions.cs

@@ -33,10 +33,28 @@ public static double DiceCoefficient(this string input, string comparedTo)
 		/// <returns></returns>
 		public static double DiceCoefficient(this string[] nGrams, string[] compareToNGrams)
 		{
-			int matches = nGrams.Intersect(compareToNGrams).Count();
-			if (matches == 0) return 0.0d;
-			double totalBigrams = nGrams.Length + compareToNGrams.Length;
-			return (2 * matches) / totalBigrams;
+			var bgCount1 = input.Length - 1;
+			var bgCount2 = comparedTo.Length - 1;
+			if (comparedTo.Length < input.Length)
+			{
+				var tmp = input;
+				input = comparedTo;
+				comparedTo = tmp;
+			}
+			var matches = 0;
+			for (var i = 0; i < input.Length - 1; i++)
+			for (var j = 0; j < comparedTo.Length - 1; j++)
+			{
+				if (input[i] == comparedTo[j] && input[i + 1] == comparedTo[j + 1])
+				{
+					matches++;
+					break;
+				}
+			}
+			if (matches == 0)
+				return 0.0d;
+
+			return 2.0 * matches / (bgCount1 + bgCount2);
 		}
 
 		public static string[] ToBiGrams(this string input)