make timestamp field an option for SsbMessageKVT and derive eq where partialeq is already derived

src/messages.rs

@@ -32,7 +32,7 @@ pub struct SsbMessageValue {
 }
 
 /// Message content types.
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Eq, PartialEq)]
 #[allow(missing_docs)]
 pub enum SsbMessageContentType {
     About,
@@ -99,6 +99,6 @@ impl SsbMessageValue {
 pub struct SsbMessageKVT {
     pub key: String,
     pub value: SsbMessageValue,
-    pub timestamp: f64,
+    pub timestamp: Option<f64>,
     pub rts: Option<f64>,
 }