The [JSON-RPC specification](http://www.jsonrpc.org/specification) allows passing parameters as an Array, for by-position
arguments, or an Object, for by-name arguments.
This implements by-name arguments, but preserves full backwards compatibility. API using by-name arguments are
easier to extend, and easier to use (no need to guess which argument goes where).
Named are mapped to positions by a per-call structure, provided through the RPC command table.
Missing arguments will be replaced by null, except if at the end, then the argument is left out completely.
Currently calls fail (though not crash) on intermediate nulls, but this should be improved on a per-call basis later.
Also introduce UniValueType
UniValueType is a wrapper for UniValue::VType which allows setting
a typeAny flag. This flag indicates the type does not matter.
(Used by RPCTypeCheckObj)
Split out methods to every module, apart from 'help' and 'stop' which
are implemented in rpcserver.cpp itself.
- This makes it easier to add or remove RPC commands - no longer everything that includes
rpcserver.h has to be rebuilt when there's a change there.
- Cleans up `rpc/server.h` by getting rid of the huge cluttered list of function definitions.
- Removes most of the bitcoin-specific code from rpcserver.cpp and .h.
Continues #7307 for the non-wallet.
Creates the generatetoaddress rpc which is virtually identical to the generate rpc except that it takes an argument for the address to mine to. It does not rely on wallet functionality.
The mining code shared by generate and generatetoaddress has been moved to another method to reduce duplication.
