Generate javadoc for augments

Modern versions of default doclet are generating this warning:

[WARNING] /home/nite/odl/mdsal/binding/mdsal-binding-test-model/target/generated-sources/BindingJavaFileGenerator/org/opendaylight/yang/gen/v1/urn/test/opendaylight/bug/_5524/module1/rev160101/uses/grouping/augmet/testgrouping/outer/ContainerAugmet11.java:17: warning: no comment
[WARNING] public interface ContainerAugmet11
[WARNING] ^

Since normal interfaces already include documentation, this seems to be an omission in mdsal-binding-generator's AbstractAugmentGenerator.createTypeImpl. Generated javadoc should include a reference to the augmentation target, module name as well as the corresponding "augment foo" YANG snippet.