Add subxt_signer crate for native & WASM compatible signing (#1016)

* Add and use subxt-signer crate for WASM compatible signing

* cargo fmt

* dev keypairs already references

* WIP fix various breakages

* re-jig features to be simpler and various test fixes etc

* doc and web fix

* fix various bits and pieces

* fix a test I broke

* dev-deps can't be linked to in docs, hrmph

* cargo fmt

* another doc link

* document the subxt_signer crate more thoroughly

* move feature flag for consistency

* more docs, no default subxt feature flag on signer, update release instrs

* Add missing license header

* unwrap_inner => into_inner

* extend a test a little to better check derive junctions

* note more clearly that the crypto bits come from sp_core::crypto

subxt/src/events/events_type.rs

@@ -19,7 +19,7 @@ use std::sync::Arc;
 /// A collection of events obtained from a block, bundled with the necessary
 /// information needed to decode and iterate over them.
 #[derive(Derivative)]
-#[derivative(Debug(bound = ""), Clone(bound = ""))]
+#[derivative(Clone(bound = ""))]
 pub struct Events<T: Config> {
     metadata: Metadata,
     block_hash: T::Hash,
@@ -31,6 +31,18 @@ pub struct Events<T: Config> {
     num_events: u32,
 }
 
+// Ignore the Metadata when debug-logging events; it's big and distracting.
+impl<T: Config> std::fmt::Debug for Events<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Events")
+            .field("block_hash", &self.block_hash)
+            .field("event_bytes", &self.event_bytes)
+            .field("start_idx", &self.start_idx)
+            .field("num_events", &self.num_events)
+            .finish()
+    }
+}
+
 impl<T: Config> Events<T> {
     pub(crate) fn new(metadata: Metadata, block_hash: T::Hash, event_bytes: Vec<u8>) -> Self {
         // event_bytes is a SCALE encoded vector of events. So, pluck the