MetricRegistryMetricReader’s fields where neither final, nor volatile
but could be accessed on multiple threads. This lead to visibility
problems where the value of a field would unexpectedly be null, causing
an NPE.

This commit updates all of the fields to declare them as final, thereby
ensuring that their values are guaranteed to be visible across different
threads.

Fixes gh-2590

Fixes gh-2567

Closes gh-2539

Update SpringApplicationContextLoader to configure test property
locations before the ApplicationContext is actually started.

Fixes gh-2198

Previously, MongoProperties did not consider the configuration of a
custom authentication database when creating a MongoClient. This
commit updates MongoProperties to use the authentication database
when it is configured, falling back to the normal database when it is
not configured.

Closes gh-2562

* elasticsearch:
  Remove unnecessary if statement

* javadoc:
  Fix Javadoc

Fixes gh-2443

Update SpringApplicationContextLoader to support @TestPropertySource
location attributes.

Fixes gh-2198

Add a `security.basic.authorize-mode` property that can be used to
affect how basic security authorization is applied.

Fixes gh-2462

Rename `spring.favicon.enabled` to `spring.mvc.favicon.enabled`.

See gh-2377

* docs:
  Improve documentation

Closes gh-2553

Closes gh-2554

Closes gh-2242

Simplify the MustacheEnvironmentCollector so that it no longer binds
the Spring Environment to a Map.

See gh-2242

Provide details of how to configure Gradle, including the work-around
require to parse any additional metadata files.

Fixes gh-2316

Fix automatic '/' -> 'index.html' forwarding to also work when a
`server.servlet-path` property is set.

Fixes gh-2351

* pull2479:
  Supported relaxed binding on inner classes

Update RelaxedDataBinder to support relaxed binding to inner classes
in the same way as normal configuration objects.

e.g. `nested.foo_bar` => `nested.fooBar`

Fixes gh-2463
Closes gh- 2479