integrate support for amd into the skrollr

check to see if require.js in available and if so, expose skrollr as a module; else put it on the global scope

add an amd example using require.js to load skrollr

require.js is added in scripts + main configuration module (standard require.js jazz)

add tests for skrollr loading

test that skrollr behaves accordingly based on the environment. require.js script is bundled in the test folder

tell grunt to run skrollr loading tests during the build

remove unused divs + styling in loading tests

use single-line comment in module definition section

remove jshint inline command and use globals config section in Grunt file

adjust if statement formatting

update readme with a note on require.js