Fix links in reference documentation.

Primarily references to Spring Framework docs and one https update.

Fixes #2218.

Author: odrotbohm

src/main/asciidoc/configuring-cors.adoc

@@ -3,7 +3,7 @@
 
 For security reasons, browsers prohibit AJAX calls to resources residing outside the current origin. When working with client-side HTTP requests issued by a browser, you want to enable specific HTTP resources to be accessible.
 
-Spring Data REST, as of 2.6, supports https://en.wikipedia.org/wiki/Cross-origin_resource_sharing[Cross-Origin Resource Sharing] (CORS) through https://docs.spring.io/spring-framework/docs/{springVersion}/reference/html/web.html#mvc-cors[Spring's CORS] support.
+Spring Data REST, as of 2.6, supports https://en.wikipedia.org/wiki/Cross-origin_resource_sharing[Cross-Origin Resource Sharing] (CORS) through link:{springDocsUrl}/web.html#mvc-cors[Spring's CORS] support.
 
 [[customizing-sdr.configuring-cors.config]]
 == Repository Interface CORS Configuration
@@ -35,7 +35,7 @@ The preceding example enables CORS support for the whole `PersonRepository` by p
 [[customizing-sdr.configuring-cors.controller-config]]
 == Repository REST Controller Method CORS Configuration
 
-Spring Data REST fully supports https://docs.spring.io/spring-framework/docs/{springVersion}/reference/html/web.html#mvc-cors-controller[Spring Web MVC's controller method configuration] on custom REST controllers that share repository base paths, as the following example shows:
+Spring Data REST fully supports link:{springDocsUrl}/web.html#mvc-cors-controller[Spring Web MVC's controller method configuration] on custom REST controllers that share repository base paths, as the following example shows:
 
 ====
 [source, java]

src/main/asciidoc/configuring-the-rest-url-path.adoc

@@ -107,7 +107,7 @@ The preceding example results in the following link value:
 ----
 ====
 
-NOTE: These snippets of JSON assume you use Spring Data REST's default format of http://stateless.co/hal_specification.html[HAL]. You can turn off HAL, which would cause the output to look different. However, your ability to override `rel` names is totally independent of the rendering format.
+NOTE: These snippets of JSON assume you use Spring Data REST's default format of https://stateless.co/hal_specification.html[HAL]. You can turn off HAL, which would cause the output to look different. However, your ability to override `rel` names is totally independent of the rendering format.
 
 You can change the `rel` of a repository, as the following example shows:
 

src/main/asciidoc/events.adoc

@@ -85,4 +85,4 @@ public class RepositoryConfiguration {
 ----
 ====
 
-NOTE: Spring Data REST events are customized https://docs.spring.io/spring/docs/{springVersion}/spring-framework-reference/core.html#context-functionality-events[Spring application events]. By default, Spring events are synchronous, unless they get republished across a boundary (such as issuing a WebSocket event or crossing into a thread).
+NOTE: Spring Data REST events are customized link:{springDocsUrl}/core.html#context-functionality-events[Spring application events]. By default, Spring events are synchronous, unless they get republished across a boundary (such as issuing a WebSocket event or crossing into a thread).

src/main/asciidoc/intro.adoc

@@ -1,6 +1,6 @@
 [[intro-chapter]]
 = Introduction
 
-REST web services have become the number one means for application integration on the web. In its core, REST defines that a system that consists of resources with which clients interact. These resources are implemented in a hypermedia-driven way. https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web.html#spring-web[Spring MVC] and https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web-reactive.html#spring-webflux[Spring WebFlux] each offer a solid foundation to build theses kinds of services. However, implementing even the simplest tenet of REST web services for a multi-domain object system can be quite tedious and result in a lot of boilerplate code.
+REST web services have become the number one means for application integration on the web. In its core, REST defines that a system that consists of resources with which clients interact. These resources are implemented in a hypermedia-driven way. link:{springDocsUrl}/web.html#spring-web[Spring MVC] and link:{springDocsUrl}/web-reactive.html#spring-webflux[Spring WebFlux] each offer a solid foundation to build theses kinds of services. However, implementing even the simplest tenet of REST web services for a multi-domain object system can be quite tedious and result in a lot of boilerplate code.
 
 Spring Data REST builds on top of the Spring Data repositories and automatically exports those as REST resources. It leverages hypermedia to let clients automatically find functionality exposed by the repositories and integrate these resources into related hypermedia-based functionality.