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

Previously, to use a custom ConfigurableWebBindingInitializer, it was
necessary to extend WebMvcConfigurationSupport and override
getConfigurableWebBindingInitializer. This had the unwanted
side-effect of switching off the auto-configuration of Spring MVC.

This commit updates the auto-configuration to look for a
ConfigurableWebBindingInitializer bean and register it with Spring
MVC.

Closes gh-2526

Closes gh-3516

Add:

 - jackson-datatype-hibernate4
 - jackson-datatype-hibernate5
 - jackson-datatype-jdk7
 - jackson-module-parameter-names

Closes gh-3727

Closes gh-3738

Previously, PropertiesConfigurationFactory would only create a
DefaultPropertyNamePatternsMatcher that ignored case if it was
ignoring unknown fields. If the binding had a target name and
unknown fields were not being ignored the matcher would consider the
case when finding matches. This meant that SERVER_PORT would not being
to ServerProperties.port as SERVER did not match the target name,
server.

This commit updates PropertiesConfigurationFactory to use a
case-ignoring DefaultPropertyNamePatternsMatcher when binding with
a target name. The tests have also been updated to test binding both
with and without ignoring case and using either Properties or
PropertySources. The above-described matching is only performed
against PropertySources and the bug only occurred when using a target
name, making it important to test all combinations.

Closes gh-3745

The target attribute is effectively checked for null beforehand so this
additional defensive check can be removed.

Closes gh-3725

See gh-3696

Closes gh-3423

This commit adds support for using the environment to configure the
Freemarker and Velocity view resolvers to allow session overrides.

Closes gh-3410

Closes gh-3421

Following the changes made to combines the /links and /hal endpoints
into a single /actuator endpoint, a web browser accessing /actuator
would receive a 406 response if HAL browser was not on the classpath.

This commit updates the /actuator main entry point so that it will
serve JSON to a web browser when HAL browser is not on the classpath.

The actuator's embedded documentation has also been updated to reflect
the recent changes.

Closes gh-3696

The annotation processor detects `@ConfigurationProperties` bean or
method definition and merges manual meta-data. The former step will fail
with a NPE if the annotation is not present on the classpath. This could
happen if the annotation processor is added to a module that is not
actually using Spring Boot.

We now have a defensive check that skips that steps but still attempts to
merge manual meta-data if present.

Closes gh-3720

See gh-3696

For some reason, we forgot to add an attribute to customize the package
name when using spring init. This is now the case.

Closes gh-3716

See gh-3569

Fixes gh-3527

Closes gh-3569

This commit provides a single endpoint, /actuator, that serves HTML
(the HAL browser) or JSON depending on the request’s accept header
that enables discovery of all of the actuator’s other endpoints.

When the management context path is configured, the /actuator endpoint
moves to the configured path, e.g. if the management context path is
set to /management, the actuator endpoint will be available from
/management.

Closes gh-3696

See gh-3539

See gh-3557

Closes gh-3715

Closes gh-3700

Improve the documentation on using two entity managers if Spring Data is
used.

Closes gh-3433

Make it more clear that the `ErrorPage` path requires an URL mapping to
be registered.

Closes gh-3698