Core and Web chapters are important chapters in the Spring Framework
reference documentation, and splitting them in multiple files will
help to evolve the documentation while not creating too many files.

Issue: SPR-12309

The reference documentation is now organized in asciidoc bookparts.
Bookparts sections can be also put in separate files, when their
size and theme are important enough to justify that.

Documentation Layout:
```
index
  |-- overview
  |
  |-- whats-new
  |
  |-- core
  |   |-- core-beans
  |   |-- core-aop
  |-- testing
  |
  |-- data-access
  |
  |-- web
  |   |-- web-mvc
  |   |-- web-view
  |-- integration
  |
  |-- appendix
      |-- appx-spring-tld
      |-- appx-spring-form-tld
```

Supersedes and closes #641

Issue: SPR-12309

Upgrade to asciidoctor-gradle-plugin version 1.5.2.
Various syntax fixes in the index.adoc reference documentation.

When a bean is retrieved via JNDI using Java config, we apply the same
inferred more for destruction callbacks as for any other bean. If an
object from the JNDI tree has a `close` or `shutdown` method, the
context calls it when it shutdowns.

Unfortunately, we have no way to know that the bean was retrieved via
JNDI and that its lifecycle is managed outside the application.

The documentation has been updated to reflect that problem explicitly.

Issue: SPR-12551

Deprecated CommonsPoolTargetSource (supporting commons pool 1.5+) in
favor of CommonsPool2TargetSource with a similar contract.

Commons Pool 2.x uses object equality while Commons Pool 1.x used
identity equality. This clearly means that Commons Pool 2 behaves
differently if several instances having the same identity according to
their `Object#equals(Object)` method are managed in the same pool. To
provide a smooth upgrade, a backward-compatible pool is created by
default; use `setUseObjectEquality(boolean)` if you need the standard
Commons Pool 2.x behavior.

Issue: SPR-12532

Issue: SPR-12639

 - fixed typos
 - improved grammar and punctuation
 - fixed class names

This commit adds support for a same origin check that compares
Origin header to Host header. It also changes the default setting
from all origins allowed to only same origin allowed.

Issues: SPR-12697, SPR-12685

Issue: SPR-11803

Update documentation to explicitly mention that the cache interceptor
must be fully initialized to provide the expected behavior and therefore
initialization code should not rely on this feature, i;e. typically in
PostConstruct callback.

Since the Transactional infrastructure has the exact same infrastructure,
update that section of the doc as well.

Issue: SPR-12700

This commit adds ResponseBodyEmitter and SseEmitter (and also
ResponseEntity<ResponseBodyEmitter> and ResponseEntity<SseEmitter>) as
new return value types supported on @RequestMapping controller methods.

See Javadoc on respective types for more details.

Issue: SPR-12212

Various parts of the reference manual as well as the Javadoc for
AnnotationConfigContextLoaderUtils improperly refer to "static inner
classes" even though this terminology does not exist in Java. The Java
Language Specification explicitly refers to such classes as "static
nested classes." An "inner class" must be non-static by definition.

Issue: SPR-12639

Issue: SPR-12575

Issue: SPR-12523

Issue: SPR-12570

In order to avoid breaking changed due to the upcoming SockJS 1.0
release (see SPR-12422 for more details) and link to the right
SockJS documentation version, we now explicitly specify that we
support SockJS protocol 0.3.3 and SockJS client 0.3.x.

Update the documentation to better reflect the fact that a @EnableCaching
configuration class must implement CachingConfigurer in order to provide
advanced customizations to the cache abstraction.

Update the developer guide to explicitly reference the (inferred)
constant introduced in 38e90105.

Also emphasis the fact that the (inferred) mode is enabled by default
with Java config and how to disable it if necessary.

Issue: SPR-12534

Issue: SPR-12517

Issue: SPR-12517

This commit put more emphasis on Spring Boot in the
"Getting Started" section, and update some outdated excerpts.

Using the "quotes" substitution group by default leads to side effect
when the "*" character is used. This is especially true for AOP pointcut
or for MVC mappings.

Plain verbatim might work most of the time unless you intend to highlight
a piece of code or a comment.

Issue: SPR-12456

Issue: SPR-12425

Prior to this commit, finding out how many application contexts had
been loaded within a test suite required the use of reflection and a
bit of hacking.

This commit addresses this issue by logging ContextCache statistics
whenever an application context is loaded by the Spring TestContext
Framework (TCF).

The log output can be enabled by setting the
"org.springframework.test.context.cache" logging category to DEBUG.

Issue: SPR-12409

This commit updates the documentation of the task:executor element to
reference the keep-alive flag.

Issue: SPR-12407

Issue: SPR-12389

Issue: SPR-12375

Issue: SPR-10767

Issues: SPR-12283

Issue: SPR-12370