Polish Mongo Documentation

* Externalize documentation code for testing
* Polish wording
* Start each new sentence with new line

Issue gh-430

docs/build.gradle

@@ -28,6 +28,7 @@ tasks.findByPath("artifactoryPublish")?.enabled = false
 
 dependencies {
 		testCompile project(':spring-session'),
+				project(':spring-session-data-mongo'),
 				"org.springframework.data:spring-data-gemfire:$springDataGemFireVersion",
 				"org.springframework.data:spring-data-redis:$springDataRedisVersion",
 				"org.springframework.data:spring-data-gemfire:$springDataGemFireVersion",