some definitions needed for the RLPx-v2 branch

eth_common/eth_types.nim

@@ -3,6 +3,8 @@ export stint
 
 type
   Hash256* = MDigest[256]
+  KeccakHash* = Hash256
+
   EthTime* = Time
 
   VMWord* = UInt256
@@ -13,6 +15,8 @@ type
   BloomFilter* = StUint[2048]
   EthAddress* = array[20, byte]
 
+  Difficulty* = UInt256
+
   GasInt* = int64
   ## Type alias used for gas computation
   # For reference - https://github.com/status-im/nimbus/issues/35#issuecomment-391726518
@@ -95,6 +99,8 @@ type
     startBlock*: HashOrNum
     maxResults*, skip*, reverse*: uint64
 
+  AbstractChainDB* = ref object
+
 when BlockNumber is int64:
   ## The goal of these templates is to make it easier to switch
   ## the block number type to a different representation