fixes#314 for me.
I've "tested" change by running examples (which prior to change simply
crashed), but since I did not run those examples successfuly ever before,
I don't know whether they worked as intended.
* Fix an issue where PollEventsIterator::next() would fail to return
keyboard input and mouse events immediately but instead only
return them on the next call to next()
* Inline process_generic_event() and queue_event()
Scroll deltas are calculated in X11 by comparing the current and
previous absolute values for the scroll axis when a scroll motion
event is received. If the user scrolls whilst the cursor is outside
of the window then an incorrect delta is reported when the cursor
re-enters the window.
Fix this by resetting the last-seen axis values whenever the cursor
re-enters the window.
* For the moment we're still using plain core X11 events
for handling keyboard activity, so remove the XInput2 code for that
* Small refactoring of X11 input handling and documentation fixes
Depending on the platform and device, scroll deltas may either
be represented as pixel deltas specifying the amount
in pixels to scroll or they may be expressed in 'lines' or 'chunks'
for low resolution devices (eg. a traditional mouse wheel).
Pixel deltas are currently available on OS X. X11 currently
supports only integer line deltas, though pixel deltas
are available via XInput2. Windows supports fractional
line deltas.
