Support using alwaysDo to automatically document every MockMvc call

The MVC test framework provides an alwaysDo method which allows the
configuration of a result handler to be that will be invoked for every
call to perform. Previously, this method could not be used for
producing documentation snippets as the snippets would overwrite each
other.

This commit adds support for writing snippets to a parameterized
output directory. Two parameters are supported: method name and step.
Method name is the name of the currently executing test method. Step
is a count of the number of calls to MockMvc.perform that have been
made in that method.

Closes gh-14

samples/rest-notes-spring-data-rest/src/test/java/com/example/notes/ApiDocumentation.java

@@ -39,7 +39,7 @@ import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.SpringApplicationConfiguration;
 import org.springframework.hateoas.MediaTypes;
-import org.springframework.restdocs.RestDocumentationConfigurer;
+import org.springframework.restdocs.config.RestDocumentationConfigurer;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 import org.springframework.test.context.web.WebAppConfiguration;
 import org.springframework.test.web.servlet.MockMvc;