Specify animation duration on individual links

Adds support for data-menu-duration attribute

@@ -15,6 +15,7 @@
Add MENU_DURATION_ATTR variable

@@ -132,10 +133,18 @@
Check if MENU_DURATION_ATTR atrribute is set on link.
If so, set animationDuration to attribute value, else use _duration() function

Signed-off-by: David Benson <dmbenson1978@gmail.com>

Reponse to pull request comments

index.html
@@ -15,6 +15,7 @@
Add data-menu-duration example to demo

src/skrollr.menu.js
@@ -133,12 +133,11 @@

Add base declaration to parseInt
Declare animationDuration earlier
Change menuDuration check to isNaN()

Signed-off-by: David Benson <dmbenson1978@gmail.com>