Cannot spend coinbase for N blocks (#111)

* use head_header in add_to_memory_pool
* add COINBASE_MATURITY const to consensus
* add coinbase maturity (wip) validaton rule to validate_block
* add coinbase maturity check to validate_block
* map errors in adapters - specific errors still wip
* reworked so adapter translates chain errors to pool errors (core errors not required)
* add test for spending immature coinbase in memory pool
* wip - add test to cover spending coinbase output in chain.process_block
* added test coverage around process_block - we have a problem with coinbase output commitments
* add a comment on the failing test
* process_block will now fail validation if we attempt to spend coinbase that has not yet matured
(remember to use a new reward_key for every block). test coverage in place to verify this

api/src/endpoints.rs

@@ -76,11 +76,11 @@ impl ApiEndpoint for OutputApi {
 		debug!("GET output {}", id);
 		let c = util::from_hex(id.clone()).map_err(|_| Error::Argument(format!("Not a valid commitment: {}", id)))?;
 
-    match self.chain.get_unspent(&Commitment::from_vec(c)) {
-      Some(utxo) => Ok(utxo),
-      None => Err(Error::NotFound),
-    }
-
+		// TODO - can probably clean up the error mapping here
+		match self.chain.get_unspent(&Commitment::from_vec(c)) {
+			Ok(utxo) => Ok(utxo),
+			Err(_) => Err(Error::NotFound),
+		}
 	}
 }