The context related parts of _GLFWwndconfig have been moved to
_GLFWctxconfig and given better names. Window hint and attribute
members have been renamed to match.
The default behavior of WGL, EGL and GLX is to choose a config that has
/at least/ the specified number of bits, whereas the GLFW 2 behavior was
to choose the closest match with very few hard constraints. Moving the
responsibility of finding the supported minimum values to the client was
problematic, as there's no way to enumerate supported configurations,
forcing the client to perform multiple (and slow) window/context
creation attempts. Not even the currently set defaults (24-bit color
and depth, 8-bit stencil) is universally supported, as bug reports show.
Renamed _glfwLibrary to _glfw and made all substructs lower-case, making
global variable names easier to read and type. Partially inspired by the
internal naming conventions of glwt.
