feat: allow arbitrary tag queries

This is an experimental feature, outside of any NIP, that demonstrates
generic tag queries.

Instead of limiting subscription filters to just querying only "e" or
"p" tags (via `#e` or `#p` attributes), any tag can be queried.

As an example, consider an event which uses a tag "url".  With this
modification, a subscription filter could add a top-level field
"#url", with an array of strings as the key.  Exact matches would be
returned.

A NIP is forthcoming to formalize this.

src/event.rs

@@ -193,39 +193,8 @@ impl Event {
         serde_json::Value::Array(tags)
     }
 
-    /// Get a list of event tags.
-    pub fn get_event_tags(&self) -> Vec<&str> {
-        let mut etags = vec![];
-        for t in self.tags.iter() {
-            if t.len() >= 2 && t.get(0).unwrap() == "e" {
-                etags.push(&t.get(1).unwrap()[..]);
-            }
-        }
-        etags
-    }
-
-    /// Get a list of pubkey/petname tags.
-    pub fn get_pubkey_tags(&self) -> Vec<&str> {
-        let mut ptags = vec![];
-        for t in self.tags.iter() {
-            if t.len() >= 2 && t.get(0).unwrap() == "p" {
-                ptags.push(&t.get(1).unwrap()[..]);
-            }
-        }
-        ptags
-    }
-
-    /// Check if a given event is referenced in an event tag.
-    pub fn event_tag_match(&self, eventid: &str) -> bool {
-        self.get_event_tags().contains(&eventid)
-    }
-
-    /// Check if a given event is referenced in an event tag.
-    pub fn pubkey_tag_match(&self, pubkey: &str) -> bool {
-        self.get_pubkey_tags().contains(&pubkey)
-    }
-
     /// Generic tag match
+    // TODO:  is this used anywhere?
     pub fn generic_tag_match(&self, tagname: &str, tagvalue: &str) -> bool {
         match &self.tagidx {
             Some(idx) => {