Introduce no-std example for extrinsic creation

[haerdib]

Probably best without any Api struct . And to test it, a separate std part where the extrinsic gets sent would be awesome.

E.g.

// no-std
fn create_extrinisc() {
     // create extrinsic completely without any api
}

// std
fn run_send_extrinisc() {
     // execute create_extrinisc and send it to node (with Api struct)
}