This updates the minimal supported version of CMake to 3.16, which in turn enables us to use more CMake features and have a cleaner build system.
This is the version that provides most new features and also the one we use in our latest docker image for CI.
Changes on the ledc_init function
Review on the README, docs and example functions
Added how to set freq and duty on README
Fix on the ledc.rst docs in the App Example
Added new example reference in the Chinese docs