Shifted the documentation away from the term 'named keys' as something
different than keys that glfwGetKeyName will return a name for. The
already existing term 'key token' should now be used to refer to the
GLFW_KEY_* constants.
The associated term 'named mouse button' was also replaced with
'supported mouse button'.
The parts explaining which key tokens will return a valid scancode from
glfwGetKeyScancode have hopefully been clarified. This issue was
reported in #2055.
The GLFW_KEY_UNKNOWN constant has been moved out of the list of key
tokens to simplify and hopefully clarify the related documentation.
Various other keyboard key related edits were made, hopefully resulting
in improvements.
Related to #2055
9959dc69ca
