HTTP RPC: modify server to handle http requests
rpcwrap: added better documentation and context creator func
rpcplus: splitted ServeCodecWithContext into two functions

ServeCodecWithContextOnce will be able to handle only one rpc request and send the response
Revert: rpcplus: splitted ServeCodecWithContext into two functions
rcpwrap: use package's ServeRequestWithContext func
rpcplus: added tests for http rpc server