simple.viewer - Modifying callback API to pass viewer info
simple.viewer - Modifying callback API to pass viewer info

We now pass viewer state to reshape, grid and axis callback (and
eventually display and keyboard in future).   This changes callback
API; if it becomes a problem, we'll add arity check to the callback
to support backward-compatible callbacks.  Let's see.

Hamayama/Gauche-gl,Hamayama/Gauche-gl,shirok/Gauche-gl,shirok/Gauche-gl