Documented X11 cursor positioning caveat.

Closes #129.
Removed option to disable loading of winmm.
Window class cleanup.
Internal header cleanup.
Documented use of deprecated OS X function.
Clarified comments for X11 key repeat hack.
Added compatibility paragraphs on flush control.
Merged clipboard code into input.
wayland: Support for setting a cursor image

Closes #346.
Removed duplicate inclusion of client header.
Removed racy checks of cached iconification state.
Made queries use XRRGetScreenResourcesCurrent.

Fixes #347.
Closes #351.
Added GLFW_FOCUSED window hint.

Fixes #101.
Fixed incorrect full screen window placement.

Fixes #213.
Fixed gamma functions acting on whole desktop.

Fixes #336.
Fixed monitor size using wrong incorrect value.

The display device string was used, instead of the adapter device name,
leading to the wrong incorrect physical size being returned for
non-primary monitors.  The right incorrect physical size is now returned
for all monitors.
Enabled enumeration of mirroring displays.

This exposes all monitors in every mirroring group, which is needed for
robust detection of an Oculus Rift.
Expose display device name as UTF-8.

This makes interaction with libOVR simpler, as it provides the display
device name in the same encoding.
Merge remote-tracking branch 'upstream/master'