[docs] Fix various syntax and rendering errors (#1001)

* fix various syntax and rendering issues

* more fixes

Author: colleenmcginnis

docs/reference/transport/rest-client/sniffer/maven_repository.md

@@ -29,7 +29,7 @@ Here is how you can configure the dependency using maven as a dependency manager
 
 Here is how you can configure the dependency using gradle as a dependency manager. Add the following to your `build.gradle` file:
 
-```groovy
+```groovy subs=true
 dependencies {
     compile 'org.elasticsearch.client:elasticsearch-rest-client-sniffer:{{version}}'
 }

docs/reference/transport/rest-client/usage/maven.md

@@ -31,7 +31,7 @@ Here is how you can configure the dependency using maven as a dependency manager
 
 Here is how you can configure the dependency using gradle as a dependency manager. Add the following to your `build.gradle` file:
 
-```groovy
+```groovy subs=true
 dependencies {
     compile 'org.elasticsearch.client:elasticsearch-rest-client:{{version}}'
 }

docs/reference/transport/rest-client/usage/requests.md

@@ -163,20 +163,17 @@ Cancellable cancellable = restClient.performRequestAsync(
     new ResponseListener() {
         @Override
         public void onSuccess(Response response) {
-            <1>
+          // Process the returned response, in case it was
+          // ready before the request got cancelled
         }
 
         @Override
         public void onFailure(Exception exception) {
-            <2>
+          // Handle the returned exception, which will most
+          // likely be a `CancellationException` as the request
+          // got cancelled
         }
     }
 );
 cancellable.cancel();
 ```
-
-1. Process the returned response, in case it was ready before the request got cancelled
-2. Handle the returned exception, which will most likely be a `CancellationException` as the request got cancelled
-
-
-