Google Custom Search Module 2.0.

# Based on Google Custom Search Engine (CSE)
- https://developers.google.com/custom-search/docs/element
- Search form provides a parameter `q` for the search query.
- Results are displayed in associated page /gcse2 (using <gcse:searchresults-only> )

# Settings
- edit the `site/modules/google_search_20/config/google_search_20.json` file, and set the value `gcse.search_engine_id`.

# How to get a Custom Search engine ID?
- See https://support.google.com/customsearch/answer/2649143?hl=en
- https://cse.google.com/all
