Moved missing defs from rubinus.rb to kernel.rb.
Started refactoring method calls in the VM.

Instead of doing everything in `on_*` and `after_*` callbacks the various
method call handlers are being moved into their own classes.

This commit also introduces the ability to skip processing the child nodes of a
given node using RubyLint::Iterator#skip_child_nodes!. See the documentation of
this method for more information.
Explicitly disable fatal parser errors.

This is due to the change in the following commit: <http://git.io/cA8ijg>.
Refactored the handling of alias/alias_method.
Support for the attr_* method family.