Change the scrolling logic.

Add a scroll handler to handle the previously unhandled events,
and remove updateBarSizeAndPosition() where it's not needed anymore.
Implemments Home, End, pageUp, pageDown and Spacebar
Merge pull request #92 from asiviero/master

Implement Home, End, Page Up, Page Down and Spacebar.
Add an example about the callback to check if it reaches the end.
Add a getEventClassName() function.

Each scrollbar object should have its own event class name. Unless,
When the one scrollbar is destroyed, another one's event will be
unbinded too.

The getEventClassName() function returns a unique event class name.
Release 0.4.7.

1. Don't prevent the default scrolling for the inactive axis.
2. Enhance the scrolling logic.
3. Implement Home, End, Page Up, Page Down and Spacebar for the key
   scrolling.
4. Bug fixes.
CSS fixes for IE.
Fix the bug that scrollbar rails show when they shouldn't.

Now, the scrollbar rails show even if the content is smaller than the
container. This patch fixes it.
Release 0.4.8.

1. Bug fixes.
Update jquery-mousewheel to 3.1.9
Merge pull request #97 from le717/patch-1

Update jquery-mousewheel to 3.1.9.
Change delta calculation in mousewheel handler.

The new version of jquery-mousewheel's delta values are changed,
and should use the new calculation for the values.