Usage on esp-idf platform

[valerio-vaccaro]

Problem

Solve issue https://github.com/olikraus/ucglib/issues/111

Solution proposed

The library can be used on ESP32 devices using the ESP-IDF platform, in order to do it it's needed to add the component.mk file like proposed in this pull request.

external documentation

The ESP-IDF platform documentation is available here.

Let me know if something is not clear.