Support custom NotNull annotations

[VladRassokhin]

It would be nice to process:

• org.eclipse.jdt.annotation.(NotNull|Nullable|NotNullByDefault) and other annotations
• javax.validation.constraints.NotNull
• edu.umd.cs.findbugs.annotations.NonNull
• javax.annotation.Nonnull
• lombok.NonNull
• FindBugs

and others.

Related:

• http://stackoverflow.com/questions/4963300/which-notnull-java-annotation-should-i-use
• http://blogs.jetbrains.com/idea/2011/03/more-flexible-and-configurable-nullublenotnull-annotations/