This combines two enhancements to the ledger_data RPC
command and related commands.
The ledger_data RPC command will now return the ledger header
in the first query (the one with no marker specified).
Also, ledger_data and related commands will now provide the
ledger header in binary if binary output is specified.
Modified existing ledgerdata unit test to cover new functionality.
* Force jtx to request/receive the 2.0 API
* Force the JSON and WebSocket tests to use 2.0 API
* This specifically allows the Websocket to create 2.0 json/ripple
and get back a 2.0 response.
* Add test for malformed json2
* Add check for parse failure
* Add check for params to be in array form.
* Correct type-o discovered in tests due to stricter checking.
* Add API version to the WSClient & JSONRPCClient test
* Update source.dox with more headers