Per the [Asciidoctor docs][0], Asciidoctor replaces the following
syntax with double arrows in the rendered HTML:
* => renders as ⇒
* <= renders as ⇐
This escapes several unintended replacements, such as in the Painless
docs.
Where appropriate, it also replaces some double arrow instances with
single arrows for consistency.
[0]: https://asciidoctor.org/docs/user-manual/#replacements
* Fix "Description"s for various sections in the functions pages.
* Added a TIP for searching using a routing key.
* Other small polishings
(cherry picked from commit 9fad0b1ac4409a42c435ed040f41cbaea18930a3)
Rest docs page update
- have the section be on separate pages
- add an Overview page
- add other formats examples
(cherry picked from commit 309bd691ff3f8625f67ca09fc1dd8e265f7e6c92)