add simple fuzz test

This is about as minimal as it gets, but it was enough to catch #54.

It's a bit weird to have a file called fuzz_test.go
and another called fuzzy_test.go.
I guess that's life in a fuzzy matching project.

fuzzy/fuzz_test.go

@@ -0,0 +1,34 @@
+package fuzzy
+
+import (
+	"sort"
+	"testing"
+)
+
+func FuzzFind(f *testing.F) {
+	f.Fuzz(func(t *testing.T, n string, h []byte) {
+		s := make([]string, len(h))
+		for i, b := range h {
+			s[i] = string(b)
+		}
+		Find(n, s)
+		FindFold(n, s)
+		FindNormalized(n, s)
+		FindNormalizedFold(n, s)
+		r := RankFind(n, s)
+		sort.Sort(r)
+		// No need to sort the other Rank calls;
+		// assume first sort can catch any bugs.
+		RankFindFold(n, s)
+		RankFindNormalized(n, s)
+		RankFindNormalizedFold(n, s)
+		if len(s) > 0 {
+			x := s[0]
+			LevenshteinDistance(n, x)
+			Match(n, x)
+			MatchFold(n, x)
+			MatchNormalized(n, x)
+			MatchNormalizedFold(n, x)
+		}
+	})
+}