axon/axon-rpc events

This solves https://github.com/Unitech/pm2-interface/issues/4

the *disconnect* event never gets fired:

    sub_sock.on('disconnect', function() {
       //never
        log('Error4');
        self.emit('close');  //never .
      });
      
we need to listen the **close** event:

     sub_sock.on('close', function() { ... });

to test:

    var ipm2 = require('pm2-interface')(); // ready events
    ipm2.on('rpc_sock:ready', function() {
        console.log('rpc_sock:ready');
    });
    ipm2.on('rpc_sock:closed', function() {
        console.log('rpc_sock:closed');
    });
    
    ipm2.on('rpc_sock:reconnecting', function() {
        console.log('rpc_sock:reconnecting');
    });
    ipm2.on('sub_sock:ready', function() {
        console.log('sub_sock:ready');
    });
    ipm2.on('sub_sock:closed', function() {
        console.log('sub_sock:closed');
    });
    
    ipm2.on('sub_sock:reconnecting', function() {
        console.log('sub_sock:reconnecting');
    });
    
    ipm2.disconnect(); // close events
    
    
testing reconect events:

do `pm2 kill` and restart the process.