Metadata V16: Be more dynamic over which hasher is used. (#1974)

* Use DynamicHasher256 to support Blake2 or Keccack depending on chain

* remove Config::Hash associated type, replace with HashFor<Config> alias

* Fix doc links

* fix wasm tests

* Don't strip system pallet associated types. check System.Hashing, not Hash. Rename BlockHash trait to Hash

* Tweak comment

* fmt

* fix merge

* Fix typo

subxt/examples/setup_config_custom.rs

@@ -3,7 +3,7 @@ use codec::Encode;
 use subxt::client::ClientState;
 use subxt::config::{
     transaction_extensions::Params, Config, ExtrinsicParams, ExtrinsicParamsEncoder,
-    ExtrinsicParamsError,
+    ExtrinsicParamsError, HashFor,
 };
 use subxt_signer::sr25519::dev;
 
@@ -15,7 +15,6 @@ pub mod runtime {}
 pub enum CustomConfig {}
 
 impl Config for CustomConfig {
-    type Hash = subxt::utils::H256;
     type AccountId = subxt::utils::AccountId32;
     type Address = subxt::utils::MultiAddress<Self::AccountId, ()>;
     type Signature = subxt::utils::MultiSignature;
@@ -28,7 +27,7 @@ impl Config for CustomConfig {
 // This represents some arbitrary (and nonsensical) custom parameters that
 // will be attached to transaction extra and additional payloads:
 pub struct CustomExtrinsicParams<T: Config> {
-    genesis_hash: T::Hash,
+    genesis_hash: HashFor<T>,
     tip: u128,
     foo: bool,
 }