add MarshalJSON and UnmarshalJSON to BitArray (#200)

See CHANGELOG

common/string.go

@@ -57,3 +57,18 @@ func SplitAndTrim(s, sep, cutset string) []string {
 	}
 	return spl
 }
+
+// Returns true if s is a non-empty printable non-tab ascii character.
+func IsASCIIText(s string) bool {
+	if len(s) == 0 {
+		return false
+	}
+	for _, b := range []byte(s) {
+		if 32 <= b && b <= 126 {
+			// good
+		} else {
+			return false
+		}
+	}
+	return true
+}