Standardizing h3/h4/h4 interface and dictionary markup. See Issue #2316 (#2317)

* Standardizing h3/h4 interface markup. Fixes #2316

* Fixing bikeshed errors

* Standardizing h4/h5 dictionary markup.

* Fix IIRFilterOptions header

Co-authored-by: Deployment Bot (from Travis CI) <[email protected]>

Author: skratchdot