Announcing availability for latest Micropython with esp-idf v4.2

Latest Micropython uses CMake build system for building esp-idf v4.2 (and later, probably).

lv_micropython dev branch is now aligned to latest Micropython and builds LVGL together with the different bindings (to LVGL, lodepng, espidf) using CMake.

Note that building the ESP32 port on the dev branch now requires CMake (v3.18 or later) and ninja installed.

The plan is to merge this change to the main branch together with LVGL v8 bindings when ready.