Add additional code block linters

[GuySartorelli]

Right now we line js code blocks and php code blocks - but our documentation also includes json and yaml, and potentially others.

We should add linters for those code blocks as well, to ensure they are (at a minimum) well formed.

Note that while JSON doesn't allow comments, some of our json code blocks may include comments as a form of documentation, which should be allowed by any JSON linter we add.