Make GetKey(win, KEY_ESCAPE) == PRESS work

[cmcaine]

GetKey is defined to return a Bool

GLFW.jl/src/glfw3.jl

Line 648 in e8d5815

GetKey(window::Window, key) = Bool(ccall((:glfwGetKey, libglfw), Cint, (Window, Cint), window, key))

, but in the documentation it is defined as returning PRESS or RELEASE. In C that doesn't matter because true, false PRESS and RELEASE are all integers and RELEASE is equal to false. But in Julia these are different types and so e.g. GLFW.GetKey(window, GLFW.KEY_ESCAPE)) == GLFW.PRESS will always return false.

This breaks the example in the Readme of GLAbstraction.jl:

    if GLFW.GetKey(window, GLFW.KEY_ESCAPE) == GLFW.PRESS
        GLFW.SetWindowShouldClose(window, true)
    end

The method added in this PR tells Julia how to compare an Action and a Bool so that code calling GetKey as documented will work as expected, while also not breaking existing code that expects GetKey to return a Bool (e.g. the code in #163).

Julia will do slightly more work when comparing Bool and Action than when comparing two Bools because it will expand the Bool to 32 bits first. This could be avoided by defining the basetype of the Action enum as UInt8, but that would be a breaking change if arrays of Action are ever passed to C (I don't think they would be, but idk).

I tried to persuade Julia to omit the expansion to 32 bits, but I couldn't find anything that worked. Closest was b == unsafe_trunc(Bool, a), but that still emits more instructions than comparing two Bools.

[cmcaine]

Hi, this is a gentle reminder that this small PR exists. I appreciate that you're probably busy and I'll just bump this PR every once in a while to increase your chances of seeing it.

[SimonDanisch]

Thank you!