Raise the bar for module `DOCUMENTAION`
This validator update was used to find the issues in https://github.com/ansible/ansible/pull/22297/files
**Validation**
* Updated Validation and docs to enforce more (items fixed in https://github.com/ansible/ansible/pull/22297/files)
* Use `suboptions` to document complex options
* Validate module name
* Validate deprecated modules have correct ANSIBLE_METADATA
**Module Documentation Generation**
* Document `suboptions:` Example https://gist.github.com/gundalow/4bdc3669d696268328ccc18528cc6718
* Tidy up HTML generation (valid HTML, no empty lists, etc)
**Documentation**
* Clarify the steps for deprecating a module
* Use correct RST headings
* Document `suboptions:` (options)
* Document `contains:` (returns)
**Details**
The aim is to get this (and corresponding module updates) complete by the time `devel` becomes `2.4`, as this allows us to raise the bar for new modules
Example `suboptions` https://gist.github.com/gundalow/4bdc3669d696268328ccc18528cc6718
The aim is to get this PR integrated into `devel` *before* we branch `stable-2.3`, this will allows us to:
* Raise the bar for new modules in 2.4
* Ensure the generated module documentation for 2.3 and higher is improved, important as we will be doing versioned docs moving forward.
* Update validate-modules
* Validates ANSIBLE_METADATA
* Ensures imports happen after documentation vars
* Some pep8 cleanup
* Clean up some left over unneeded code
* Update modules for new module guidelines and validate-modules checks
* Update imports for ec2_vpc_route_table and ec2_vpc_nat_gateway
