Make CachingGenerator public

Needed at this moment because generated parser classes need access to its
enclosed Arguments class. Ideally the latter should be exported to its own
class.
build.gradle: update asm dependency to 4.2, add javadoc link
ParserTransformer: offer the option to dump the bytecode of a parser class

This will allow usage of procyon, in another package to be created, to dump the
source of a parser.

Unfortunately, since procyon is 1.7+, it cannot be used in this package. Well,
good enough I guess, since at runtime we don't need debug tools.