EPIC Review documentation for best practices

[GuySartorelli]

Scope

The primary purpose of this PR is to ensure that:

• code examples exhibit best practices, including but not limited to:
  • always using namespaces, with exception of Page and PageController
  • always using ::create() instead of new for instantiating Injectable classes
  • would pass linting
• code examples are consistent
• written documentation encourages best practice, especially when documenting alternatives that should be only used if they're specifically needed to be done that way
• written documentation is clear and understandable
• written documentation always uses an API link the first time a class, method, or property is referenced on that page
• method names referenced in written documentation end with ()

Explicitly out of scope

• grammatical or spelling mistakes in existing writing
• inconsistent markdown styling
• anything else that will be covered by Add linting for docs #11

Decisions to be made:

1. Does this only apply to CMS 5 doc (like EPIC Review CMS5 doc for truthfulness #212 did) or to CMS 4 AND 5 docs?