Consider removing call to `Init` in `__init__`

[colinxs]

While it's useful to have this happen automatically, it also makes it difficult to use GLFW in a package that is running on a headless machine and only uses GLFW for a small part of it's functionality. Given that it's just a single call to Init(), would you consider removing it from __init__?

[Gnimuc]

I guess you could always set the environment variable DISPLAY=:0 to prune GLFW errors on a headless machine.

[jayschwa]

Removing Init in __init__ would be a breaking change from a semantic versioning perspective, and I'm reluctant to do that (right now). However, I don't want to totally dismiss this issue either. Some ideas:

• Apps and packages could avoid importing GLFW.jl for their code paths that do not use it.
• GLFW.jl could avoid calling Init in __init__ if it detects the presence of some global symbol or environment variable.
• GLFW.jl could remove the call to Init in __init__, but automatically call Init the first time some other function is executed, thereby preserving compatibility with existing apps or packages that will not call Init themselves.

[musm]

Option 3 seems quite sensible. We do something similar in MATLAB.jl with regards to initialization, whereby we only initialize code after an appropriate constructor is called for the first time.