Removed gevent from features, and added pyev

 * **Bidirectional:** remote function can be call by both side of the

   connection, so a client can connect to a server and export functions to it.

 * **Use Gevent:** the server mode can use Gevent to take profits of

   asynchronous io, but a threaded mode is also provided. The client mode can

   be used without Gevent or Threading.

 * **Fully event based**: sjRpc takes profits of asynchronous io, allowing a

   server to handle thousands of client connection with a reasonable memory

   usage.

 * **Multiplexed:** sjRpc can run many "protocols" on the same connection,

   read more about protocols in `Multiplexing & protocols`_ section.

 * **Fallback mode:** for compatibility with olders sjRpc.