This also adds tests to verify that the created error string follows
the expected format of "code: message" and tests to verify that Error
can be used as an error. Additionally, the idiom
var _, _ error = Error{}, &Error{}
was added so the build will fail if the builtin error interface is
never satisified in the future.
Add new RpcRawCommand to get []byte represtation of reply instead of
btcjson.Result.
Export ReadResultCommand to allow caller of RpcRawCommand to deal with
the reply in the same way RpcCommand does.
Adjust test code to for the above changes.
Add return types for serveral additional commands.
Fix required vs. optional arguments for createrawtransaction.
Update tests and test coverage for all changes.
Following the example of bitcoind and the bitcoin wiki, provide a
function to convert floats (which are returned by the json-rpc server)
to int64 (which is the normal representation for most values involving
bitcoins).
