Added verbose flag to print verbose output

[djhworld]

This makes integrating this script into other scripts that accept JSON simpler.

If users wish to see verbose output (i.e. the Sent and Received sections) they can use the -v or --verbose flag

Default output

tmp/tplink-smartplug|master ✔ ▶ python tplink-smartplug.py -t <my-ip> -c on
{"system":{"set_relay_state":{"err_code":0}}}

Verbose output

tmp/tplink-smartplug|master ✔ ▶ python tplink-smartplug.py -v -t <my-ip>  -c on
Sent:      {"system":{"set_relay_state":{"state":1}}}
Received:  {"system":{"set_relay_state":{"err_code":0}}}

[softScheck]

This function was added by another pull request.