add picturefill polyfill (fixes issue #366)
add promise polyfill (fixes issue #370)
improve picture polyfill
Update index.html for #366 and #370

Added a note about Promise #370 and Responsive Images (Picturefill) #366 polyfills; sorted lists alphabetically for easier reading.
Merge pull request #371 from AMA3/master

Master - added notes to documentation for Promise #370 and Responsive Images #366