added support of custom animation effects applied whenever viewport position is changed; some fixes in the main plugin
added new extension: jquery.scrollless.animbyscroll which implements scrolling animation effect
added new extension: jquery.scrollless.scrollbar which adds custom vertical scrollbar
some style changes in jquery.scrollless.affixnav extension
added/updated minified versions of .js files
some changes in demo.html: added "scrollbar" and "animbyscroll" extensions; removed "pagenav" extension
some changes in README file
updated Manifest file