Document GLUT:CLOSE's #+darwin call to DESTROY-WINDOW.
Merge pull request #28 from luismbo/for-3b
Move CLOSE event bookkeeping out of the high-level callback GF.

This addresses github issues #28 and #29 which describe a situation
where calling GLUT:CLOSE directly closes windows on darwin only. With
this change, the darwin-specific behaviour is only ever invoked from
the low-level callback. Since we no longer have GLUT:CLOSE methods
for the base window classes, calling GLUT:CLOSE directly will not
actually close windows on darwin (nor any other platform) and will
result in a NO-APPLICABLE-METHOD error if no methods were defined for
specific window classes.
Merge pull request #29 from luismbo/for-3b
download new .spec files
update generate-funcs.lisp for new .spec files
update low-level bindings (%GL:) to .spec version 72, gl4.2
add an example that just prints out version/extension/etc info
update gl:get* for opengl 4.2 and some non-core ARB extensions

closes #2
query more limits in gl-info example

also add :verbose t option to query everything supported by get*
fix gl:get* compiler macro
catch more errors in gl-info example
check glsl version in shader-vao example
More resilient libGL loading.
Fallback GetProcAddress bindings so things will Just Work on common configurations.
add :description to .asd file
download new .spec files
update generate-funcs.lisp for v78 .spec files
update low-level bindings (%GL:) to .spec version 78
rearrange automatic error checking a bit

theoretically it can now be used with code that has multiple threads
that each have their own gl context, if each thread binds
%GL::*IN-BEGIN*. (threads sharing a context need to share the
binding though, which probably means using the global binding)

haven't decided on an official API for that yet though, or even if
it should have one, so probably will change at some point.