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

Issue: SPR-12347

Issue: SPR-12306

Issue: SPR-12273

Issue: SPR-12270

This commit ensures that single quotes nested in double quotes in
code examples in the reference manual are properly escaped using ''.

Issue: SPR-12246

Issue: SPR-8025

Issue: SPR-7689

Issue:  SPR-7735

Issue: SPR-7725

Issue: SPR-12186

Issue: SPR-14036

Issue: SPR-12113

This change adds the artifacts names in the Spring Framework Modules
documentation. Linking both concepts make it easier to decide which
Spring module should be importer in an application's build.

Issue: SPR-11534

This commit introduces a new-in-4.1 section in the reference manual with
initial content for testing improvements.

This commit restructures the content of the "TestExecutionListener
registration and ordering" section of the Testing chapter in the
reference manual into cross-referenced subsections with more
appropriate titles.

In addition, this commit introduces a new "Merging
TestExecutionListeners" subsection which documents the new MergeMode
feature in @TestExecutionListeners, including an example demonstrating
the MERGE_WITH_DEFAULTS mode.

Issue: SPR-12083

This commit introduces a new "TestExecutionListener registration and
ordering" section in the Testing chapter of the reference manual.

Issue: SPR-12082

This commit introduces a new "Programmatic transaction management"
section in the Testing chapter of the reference manual with an example
highlighting the new support provided via TestTransaction.

In addition, this commit begins the work to be addressed more
thoroughly in SPR-11399 by overhauling the entire "Transaction
management" section with in-depth discussions on the following topics.

 - Test-managed transactions
 - Enabling and disabling transactions
 - Transaction rollback and commit behavior
 - Executing code outside of a transaction
 - Configuring a transaction manager

Issue: SPR-11941, SPR-11399

This commit introduces a new "Context configuration with test property
sources" section in the Testing chapter of the reference manual.

In addition, the "Context caching" section has been updated regarding
support for test property source locations and properties in
MergedContextConfiguration.

Issue: SPR-12076