Upgrade to Spring Boot 2.7.0 GA.

Migrate the README to asciidoctor.

Closes #636.

Author: gregturn

README.md

@@ -72,7 +72,6 @@ Local Elasticsearch instance must be running to run the tests.
 * `gridfs` - Example project showing usage of gridFS with MongoDB.
 * `jmolecules` - Example of Spring Data MongoDB working with a jMolecules based domain model.
 * `kotlin` - Example for using [Kotlin](https://kotlinlang.org/) with MongoDB.
-* `linking` - Example demonstrating possibilities for linking documents.
 * `query-by-example` - Example project showing usage of Query by Example with MongoDB.
 * `querydsl` - Example project showing imperative and reactive [Querydsl](https://github.com/querydsl/querydsl) support for MongoDB.
 * `reactive` - Example project to show reactive template and repository support.
@@ -132,4 +131,4 @@ Local Redis instances must be running to run the tests.
 * The code makes use of Java 16 language features therefore you need Java 16 or newer to
   run and compile the examples.
 * Most store modules examples start their database via Testcontainers or as
-  embedded/in-memory server unless stated otherwise.
+  embedded/in-memory server unless stated otherwise.

pom.xml

@@ -13,7 +13,7 @@
 	<parent>
 		<groupId>org.springframework.boot</groupId>
 		<artifactId>spring-boot-starter-parent</artifactId>
-		<version>2.7.0-RC1</version>
+		<version>2.7.0</version>
 	</parent>
 
 	<modules>