Refactoring of GLIR queues: 1 on each canvas.context

So now there is a queue on each gloo object, which is kept there.
The queue can be associated with other queues, creating a sort
of tree. This also got rid of the need for a shared queue.
Added shared context example
address review comments

also canvas(config, shared)
attempt to reduce segfaults
minor fixes
appveyor fix
Merge pull request #653 from almarklein/glir-queues

Glir queue refactoring