3.1.8 - ios fix - auto z-index - global settings

New features
- $.nicescroll.options, the global option object cointains init settings used from all nicescroll instances - close #172
- class .nicescroll-rails added to rails [EXPERIMENTAL]

New options
- hidecursordelay, set the delay in microseconds to fading out scrollbars (default:400) - close #151
- directionlockdeadzone, dead zone in pixels for direction lock activation (default:6)

Changed features
- Automatic z-index for rails, default value for zindex sets to "auto" - close #149 #170
- resize method no more debounced with setTimeout, use lazyResize - close #174

Fixes
- iOS scrolling problem on vertical drag
- div-into-div, quick fix for main div with position not set to "relative" - close #163