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.