Closes gh-1967

I edited for spelling, punctuation, grammar, usage,
and corporate voice.

I also added cross-references and links to the Javadoc.

I edited for the usual stuff: spelling, punctuation,
grammar, formatting, usage, and voice.

I edited for spelling, punctuation, grammar, usage, and corporate voice. I also added cross-references and links to the Javadoc in a number of places.

Issue: SPR-17095

Issue: SPR-12458

Issue: SPR-12458

Note: Some symbol combinations (including <=) serve as textual symbol
replacements in AsciiDoc.

http://asciidoctor.org/docs/asciidoc-syntax-quick-reference/#text-replacement

Issue: SPR-16602

Issue: SPR-16592

This commit adds an Asciidoc anchor to the section on different injection
styles to be able to link to the discussion as official recommendation.

Closes gh-1681

Issue: SPR-16230

Issue: SPR-16213

Issue: SPR-16142

Issue: SPR-16044

Issue: SPR-16076
(cherry picked from commit 17fb4fed)

Issue: SPR-14579

1. Move schemas to local appendix within each top-level section.
2. Link to Javadoc for JSP tags
3. Purge Class Spring usage information

Issue: SPR-16045

Closes gh-1483

Issue: SPR-15973

Issue: SPR-15793

Issue: SPR-15266

Also marks @Conditional as @Documented, aligned with other annotations.

Issue: SPR-15266

Issue: SPR-14997

This commit removes docbook from the documentation toolchain and
instead makes use of asciidoctor to render the reference documentation
in HTML and PDF formats.

The main Gradle build has been refactored with the documentation tasks
and sniffer tasks extracted to their own gradle file in the "gradle"
folder.

A new asciidoctor Spring theme is also used to render the HTML5 backend.

Issue: SPR-14997

Issue: SPR-15354

See gh-1349

Issue: SPR-14711

Issue: SPR-15154

Issue: SPR-15153

Issue: SPR-15072

Issue: SPR-14812