Fixing new caching related issue with host vars

The vars_cache was not being properly merged with the setup_cache
for all hosts, which was previously not noticed when registered
variables were stored in the setup_cache.

Fixes #8944
Fixing docs error for new region param
Test that we can override variables set in inventory when the vars_file name is templated

Fixes #8903
Prevents module from failing with "_mysql_exceptions.Warning: Sending passwords in plain text without SSL/TLS is extremely insecure." When not using SSL/TLS.
Merge pull request #8953 from jsmartin/mysql_fix

Prevents mysql_replication from failing with "_mysql_exceptions.Warning: Sending pa...
Add documentation about bin_ansible_callbacks setting.  Standardization and cleanup.
Add version_added info.
Modules are almost always written now by mutliple authors, so don't show this field on website, since it grows obsolete and does not take into account all contributors.
Contributors are still listed on github module source and in repo, and original authors still in the file for when development questions arise, but want
to funnel support questions to the mailing list versus directly to them.
Fix typo in redis cache change from 10afaee1
Convert boolean strings from set_fact to proper boolean values

Also adds integration tests for booleanification of strings

Fixes #8629
First pass at updating community page by moving CONTRIBUTING.md content onto docsite.
Fix some link formatting.
Fix sidebar notation for Galaxy.
Indents in docs.
Simplify contributing.md

Make it more likely folks will read this page :)
Update CONTRIBUTING.md
Fixing multiline parsing to preserve newlines

Fixes #8813
Include el7 mariadb support in mysql integration test
Merge pull request #8966 from jlaska/devel

Include el7 mariadb support in mysql integration test