Show and tell: RPC on embedded devices

[elcritch]

P.S. The standard ESP32 wifi example `smart_config` results in a binary that's 
`664kB`. The Nim WiFi + RPC version 
(<https://github.com/elcritch/nesper/tree/master/esp-idf-examples/simplewifi-rpc>)
 above results in a binary that's `736kB`. That means the entire Nim runtime 
and all the standard library utilities only takes about `72kB`! I'm pretty 
impressed with that result. Great job Nim team!