Add support for using REST Assured to generate documentation snippets

This commit adds a new module, spring-restdocs-restassured, that
can be used to generate documentation snippets when testing a service
with REST Assured.

Please refer to the updated reference documentation for details.

Thanks to Johan Haleby for making a change to REST Assured so that
path parameters could be documented.

Closes gh-102

docs/src/test/java/com/example/Constraints.java

@@ -41,6 +41,7 @@ public class Constraints {
 		@NotNull
 		@Size(min = 8)
 		String password;
+
 	}
 	// end::constraints[]