AnnotationLocationCheck fixed. #302
for for Javadoc build for java version 6, 'java.lang.ClassCastException: com.sun.tools.javadoc.ClassDocImpl cannot be cast to com.sun.javadoc.AnnotationTypeDoc'
Issue #49. Added ANTLR4 grammar for parsing Javadoc comments.
Issue #49. Added support of Javadoc comments. Extended API to create Javadoc Checks.
Issue #49. Added unit tests for generated parse trees of Javadoc comments