Make GetKey(win, KEY_ESCAPE) == PRESS work

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

This method tells Julia how to compare an `Action` and a `Bool` so that
code calling `GetKey` as documented will work as expected.

Julia will do slightly more work when comparing `Bool` and `Action` than
when comparing two `Bool`s 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 `Bool`s.

src/glfw3.jl

@@ -8,6 +8,15 @@
 	PRESS                  = 1
 	REPEAT                 = 2
 end
+# GetKey is defined below to return a Bool, but in the documentation it is
+# defined as returning PRESS or RELEASE. In C that doesn't matter, but in
+# Julia these are different types and so e.g.
+# `GLFW.GetKey(window, GLFW.KEY_ESCAPE)) == GLFW.PRESS` will always return
+# false.
+#
+# This method tells Julia how to compare an Action and a Bool so that code
+# calling GetKey as documented will work as expected.
+Base.(==)(b::Bool, a::Action) = b == Integer(a)
 
 @enum Key::Cint begin
 	# Unknown key