Invoke subgraph handler in watcher event processing (#34)

* Invoke subgraph handler in watcher event processing

* Fix error when invoking subgraph handler

* Parse events using event signature specified in subgraph yaml

* Use contract abi to parse event params

* Invoke event handler based on event signature

* Fill event with block and transaction data

* Comment missing fields in block and transaction data

packages/graph-node/test/subgraph/example1/subgraph.yaml

@@ -6,7 +6,7 @@ dataSources:
     name: Example1
     network: mainnet
     source:
-      address: "0x3ebd8bb51fF52aDAc490117B31F5F137BB125A9D"
+      address: "0x4Ab7aE18973491Df21d6103dfA55170fdB2CCC98"
       abi: Example1
     mapping:
       kind: ethereum/events
@@ -18,6 +18,6 @@ dataSources:
         - name: Example1
           file: ./abis/Example1.json
       eventHandlers:
-        - event: Test(string,uint256)
+        - event: Test(string,uint8)
           handler: handleTest
       file: ./src/mapping.ts