More robust event handling

If an app uses more than 1 GL context, there could be a collision during the asynchronous event handling. E.g. resize event for window1 arrives while window2 context is active, so the subsequent call to gl.viewport() doesn't work.

Added the makeCurrent() call to the class Window event handling mechanism.

Add basic canvas emulation and OSX support

Added logic for multiple canvases with separate 2d contexts
Tested OSX npm install in CI
Updated deps for Nodejs 10

GLFW Initial

The core features are estabilished.

• Class Window
• Class Document is similar to HTMLDocument
• Uses GLFW3 backend
• Exposes native handles
• Can switch screen modes
• Multiple windows