Previously, manual meta-data were added to the existing set of entries
which could lead to duplicates if a manual entry is meant to complement
a property that is detected via the processor.

We now match the name and type of the item against the auto-detected
entries. If no match is found, we add the extra entry as we did before.
If a match is found we override the description, default value and
deprecation information.

Closes gh-3562

See gh-3792

Closes gh-3792

* pr/3793:
  Fix link to exec maven plugin

Closes gh-3793

Closes gh-3787

Previously, `ResourceUrlEncodingFilter` was registered even if the
resource chain handling was disabled (which is the default).

We now take care of registering it only if the resource chain handling is
enabled.

Closes gh-3353

Given that Spring Boot uses java config accross the board, a new `value`
attribute is now aliased to the existing `classes` attribute such that
one could write the following:

@SpringApplicationConfiguration(MyConfig.class)
public class MyTest {}

Closes gh-3635

Changing the velocity view resolver to a VelocityLayoutViewResolver seems
a common use case so it has now a dedicated section in the relevant how
to.

Closes gh-3732

The default value of `spring.devtools.restart.exclude` is quite long and
any override requires to copy/paste it to add additional exclusions. To
avoid that, a new `spring.devtools.restart.additional-exclude` property
has been added.

Both properties are now used to compute the full list of exclusions that
is used by PatternClassPathRestartStrategy.

Closes gh-3774

Closes gh-3773

Prior to this commit, the devtools used bean factory post processors to
configure the environment with custom, development-time properties. This
meant that the environment was configured as part of the application
context being refreshed. Crucially, this happened after any property
conditions were evaluated making it impossible for the devtools to
change the default auto-configuration behaviour for a bean or
configuration class that was conditional on a property.

This commit moves the configuration of the environment into an
ApplicationListener that listens for the
ApplicationEnvironmentPreparedEvent which is published as soon as the
Environment has been prepared and before the application context is
refreshed.

Closes gh-3726

The commit introduces a new extension point, EnvironmentPostProcessor,
that can be implemented by classes that want to modify the
environment. Implementations of EnvironmentPostProcessor are loaded
via spring.factories and called in response to the
ApplicationEnvironmentPreparedEvent. Application listeners that wish
to work with the post-processed environment can continue to listen
to ApplicationEnvironmentPreparedEvent and order themselves to
run after EnvironmentPostProcessingApplicationListener.

Existing ApplicationListeners that modify the environment have,
where possible, been updated to implement EnvironmentPostProcessor
instead.

Closes gh-3737

Conflicts:
	spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/HealthIndicatorAutoConfiguration.java

The DataSource health indicator uses `JdbcTemplate` behind the scenes
but nothing was checking that it is actually available.

`DataSourcesHealthIndicatorConfiguration` is now disabled if
`spring-jdbc` is not on the classpath.

Fixes gh-3765

* pr/3721:
  Fix typo

Closes gh-3721

* pr/3752:
  Fix table layout

Closes gh-3752

Closes gh-3760

Closes gh-3751

Closes gh-3756

On start.spring.io, if you customize the artifactId it creates a zip file
with the same name. The `spring init` command did not have a similar
shortcut.

This commit updates the request to customize the artifactId if none is
set and a custom location was specified. Just as we check for the
presence of a dot to figure out if we have to extract the archive or not,
we check for it to generate an artifactId without an extension.

In practice, `spring init foo` creates a foo directory with a project
whose artifactId is `foo` and `spring init foo.zip` stores a foo.zip
file with the same project (i.e. the artifactId is `foo`).

Closes gh-3714

The `spring.datasource.name` property was hidden behind the 'name'
attribute of the Tomcat connection pool (since we are mapping all
datasource implementations on the `spring.datasource` namespace.

This commit replace the injected value by hand with the use of the
regular `DataSourceProperties`. That way, we generate proper meta-data
for it as well.

Closes gh-3755

A new `spring.datasource.type` property can now be used to configure the
connection pool implementation to use (rather than only relying on Boot's
preferences).

Closes gh-3705

Improve the documentation to explain the necessary steps to create a
custom Spring Boot starter. In particular, provide more details regarding
naming conventions.

Closes gh-2537
See gh-2927

* pr/3750:
  Polish
  Add fallbackToSystemLocale configuration key

Closes gh-3750

Allow to configure the `fallbackToSystemLocale` attribute of
`MessageSource` via configuration.

Closes gh-3749