ESP-Now offers a low-level adhoc network over 802.11 frames ... make this available from a nice MicroPython API.

Refs:
http://espressif.com/sites/default/files/documentation/esp-now_user_guide_en.pdf
http://esp-idf.readthedocs.io/en/latest/api-reference/wifi/esp_now.html
http://www.espressif.com/sites/default/files/documentation/2c-esp8266_non_os_sdk_api_reference_en.pdf chapter 3.8

This is related to #176 (mesh networking) and #188 (generalized packet objects)