Questions about the network implementation

I'd like to propose the following, lemme know if you're OK with me trying it out:

• define a bunch of negative numeric error codes for socket errors, use -1 as generic/unknown error
  
• update the esp8266 network code to return the appropriate error code
  
• in socketserver.c, when netrecv/netsend/netcreate return an error code enqueue an error callback on the socket or httpCRs object passing the error string corresponding to the code as argument (right now neither error callback takes any argument, so this should be backwards compatible)
  
  

Thoughts?