Fix for the GLFW backend when requesting a single video mode, previously causing a crash.
Best guess merging most recent fixes from @rougier's PyGLFW.  Some fixes seem to have been applied in both separate versions.
The assertion most be removed, and the error callback is reimplemented.
This change must have been newer, fixing an old bug?  Titles do not show up correctly otherwise, so presuming the casts to int were also more recent.  Adding the utf-8 encoding because GLFW supports it.
Fix for warning that's always shown because comparison fails, one is list the other is tuple.  Also dropped the warning level because VisPy exposes no way to get the correct fullscreen resolution without knowing the hardware.
Merge pull request #665 from alexjc/glfw-fullscreen

Fix GLFW Fullscreen Canvas Crash