Update Gruntfile.js to copy 'dist/' files to 'docs/dist/' with 'grunt dist' task; Fixes #12030: navbar toggle focus state

if affixed top add scrollTop to it position.top
calculate and cache pinnedoffset independent of scrolling for initial load

fixes #10205 Scrollspy Doesn't Support Chinese ID Targets  http://mathiasbynens.be/notes/html5-id-class

Fixes #11610: Add @grid-float-breakpoint-max to better link navbar behavior across viewports and improve customization.

Also addresses #10371, #10395, and #10465.

http://caniuse.com/#search=grad