Added eth_hashrate. (#503)

Added eth_hashrate
Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

docs/Reference/JSON-RPC-API-Methods.md

@@ -374,6 +374,35 @@ None
     }
     ```
 
+### eth_hashrate
+
+Returns the number of hashes per second with which the node is mining. 
+
+**Parameters**
+
+None
+
+**Returns**
+
+`result` : `quantity` - Number of hashes per second
+
+!!! example
+    ```bash tab="curl HTTP request"
+    $ curl -X POST --data '{"jsonrpc":"2.0","method":"eth_hashrate","params":[],"id":1}' <JSON-RPC-http-endpoint:port>
+    ```
+    
+    ```bash tab="wscat WS request"
+    {"jsonrpc":"2.0","method":"eth_hashrate","params":[],"id":1}
+    ```
+    
+    ```json tab="JSON result"
+    {
+        "jsonrpc": "2.0",
+        "id": 1,
+        "result": "0x12b"
+    }
+    ```
+
 ### eth_gasPrice
 
 Returns the current gas unit price in wei.

docs/Using-Pantheon/Mining.md

@@ -15,3 +15,4 @@ JSON-RPC API methods for mining are:
 * [`miner_start`](../Reference/JSON-RPC-API-Methods.md#miner_start) to start mining. 
 * [`miner_stop`](../Reference/JSON-RPC-API-Methods.md#miner_stop) to stop mining. 
 * [`eth_mining`](../Reference/JSON-RPC-API-Methods.md#eth_mining) to determine whether the client is actively mining new blocks.   
+* [`eth_hashrate`](../Reference/JSON-RPC-API-Methods.md#eth_hashrate) to get the number of hashes per second with which the node is mining.