Issue #2879533 by lbaran: Improve Charts code documentation

charts.api.php

charts.module

charts.permissions.yml

charts.routing.yml

charts.services.yml

includes/charts.pages.inc

modules/charts_api_example/README.txt

modules/charts_api_example/charts_api_example.info.yml

modules/charts_api_example/charts_api_example.libraries.yml

modules/charts_api_example/charts_api_example.module

modules/charts_api_example/charts_api_example.routing.yml

modules/charts_api_example/js/charts_api_example.js

...es/charts_api_example/src/Controller/ChartsApiExample.php

...charts_api_example/templates/charts_api_example.html.twig

modules/charts_c3/charts_c3.info.yml

modules/charts_c3/charts_c3.libraries.yml

modules/charts_c3/src/Charts/C3ChartsRender.php

modules/charts_google/charts_google.info.yml

modules/charts_google/charts_google.libraries.yml

modules/charts_google/charts_google.module