jsonrpc-s: new fucntion jsonrpc_exec(cmd)

- execute the jsonrpc command given as parameter
- cmd has to be a full json rpc document
- example:
    jsonrpc_exec('{"jsonrpc": "2.0", "method": "dispatcher.reload", "id": 1}')
- the cmd can be a dynamic string with variables
jsonrpc-s: new config variable $jsonrpl(key)

- access jsonrpc reply when using jsonrpc_exec(cmd)
- the key can be:
  - code - the response code as when the jsonrpc would have been executed over
  	http
  - text - the text following the code as when the jsonrpc would have
  	been executed over http
  - body - the body of the jsonrpc response - the full json document
jsonrpc-s: documentation for jsonrpc_exec(cmd)