Implement `min/max_dimensions` for x11 windows.
Implement `min/max_dimensions` for x11 windows.

Size hints are only being set for non-fullscreen windows, if
`max_dimensions` are set they'll override the normal `dimensions`
since X11 will not automatically resize the window after setting
the size hints.

`PSize` hint is currently set along with the `min/max` hints for
good measure.

tomaka/winit,tomaka/glutin,vberger/glutin,mbrubeck/glutin,mbrubeck/glutin,nc4rrillo/glutin,mitchmindtree/glutin,bvssvni/glutin,servo/glutin,ozkriff/glutin,ecoal95/glutin