Initiate initializr documentation

This commit commit adds restdocs and stub generators and initiate
a reference guide for Initializr.

Most of the controller tests now use MockMvc via a custom version
of the MockMvcClientHttpRequestFactory (from spring-test). The
snippet names are auto-generated in the form

<HttpMethod>/<path>[/queries(/<name-value)*][/headers](/name-value)*]

when there is a comma-separated value in a header it is
abbreviated as <first-value>.MORE.

Wiremock stubs are generated in the same form under
snippets/stubs (with ".json" as the
file extension).

The controller tests that stayed as full stack use a different
base class AbstractFullStackInitializrIntegrationTests.

A long JSON body can be broken out into separate snippets
for each field (or rather a list of fields supplied by the
user). This feature was already used with hard-coded snippets
in the wiki.

See gh-295

initializr-stubs/pom.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>io.spring.initializr</groupId>
+		<artifactId>initializr</artifactId>
+		<version>1.0.0.BUILD-SNAPSHOT</version>
+	</parent>
+	<artifactId>initializr-stubs</artifactId>
+	<name>Spring Initializr :: Stubs</name>
+
+	<build>
+		<plugins>
+			<plugin>
+				<artifactId>maven-jar-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>default-jar</id>
+						<!-- put the default-jar in the none phase to skip it from being created -->
+						<phase>none</phase>
+					</execution>
+				</executions>
+			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-assembly-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>stub</id>
+						<phase>prepare-package</phase>
+						<goals>
+							<goal>single</goal>
+						</goals>
+						<inherited>false</inherited>
+						<configuration>
+							<attach>true</attach>
+							<descriptor>${basedir}/src/assembly/stub.xml</descriptor>
+							<appendAssemblyId>false</appendAssemblyId>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

initializr-stubs/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>${basedir}/../initializr-web/target/snippets/stubs</directory>
+			<outputDirectory>META-INF/${project.groupId}/${project.artifactId}/${project.version}/mappings</outputDirectory>
+			<includes>
+				<include>**/*</include>
+			</includes>
+		</fileSet>
+	</fileSets>
+</assembly>