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.
* moved C++ examples to a new cxx folder in
examples
* added experimental C++ component
* added ESPException class to the C++ experimental
component
* added test cases for ESPException and
corresponding test macros