Polish contribution

Move documentation to a dedicated module (`initializr-docs`) with a test
that uses the stubs with the Spring Cloud Contract runner.

See gh-295

initializr-web/src/assembly/stub.xml

@@ -0,0 +1,19 @@
+<assembly
+	xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.3"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.3 http://maven.apache.org/xsd/assembly-1.1.3.xsd">
+	<id>stubs</id>
+	<formats>
+		<format>jar</format>
+	</formats>
+	<includeBaseDirectory>false</includeBaseDirectory>
+	<fileSets>
+		<fileSet>
+			<directory>target/snippets/stubs</directory>
+			<outputDirectory>META-INF/${project.groupId}/${project.artifactId}/${project.version}/mappings</outputDirectory>
+			<includes>
+				<include>**/*</include>
+			</includes>
+		</fileSet>
+	</fileSets>
+</assembly>