This is not necessary for correct behaviour or to have valid sdkconfig files
(previous commit adds tests for this), but it's useful for consistency with
sdkconfig files generated by menuconfig.
As reported in https://github.com/espressif/vscode-esp-idf-extension/issues/83
V2 adds:
* Independent result for visibility (showing/hiding menus)
* Includes adding IDs for all items (menus & symbols) in kconfig_menus.json
Still backwards compatible with V1, with some small changes (menu items now listed in results).
Also added some protocol docs, changed the "listening on stdin" message to come after any kconfiglib warnings
