Added unicode support

Replaced strings with rune-slices, which capture unicode codepoints more
accurately.

re_test.go

@@ -116,7 +116,7 @@ func TestFindAllMatches(t *testing.T) {
 		t.Run(test.re+"	"+test.str, func(t *testing.T) {
 			re_postfix := shuntingYard(test.re)
 			startState := thompson(re_postfix)
-			matchIndices := findAllMatches(startState, test.str)
+			matchIndices := findAllMatches(startState, []rune(test.str))
 			if !slices.Equal(test.result, matchIndices) {
 				t.Errorf("Wanted %v	Got %v\n", test.result, matchIndices)
 			}