move to position: fixed

[schlosser]

Fixes the parallax scrolling so that it doesn't mess up if you reload half way down the page.

Lessons learned:

• background-attachement: fixed is borked in chrome: http://stackoverflow.com/questions/20268962/fixed-attachment-background-image-flicker-disappear-in-chrome-when-coupled-with
• position: fixed to the rescue!

[natebrennand]

ping @RaymondXu / @eunicekokor / @evantarrh (I don't know enough CSS)

[schlosser]

@evantarrh updated

[evantarrh]

the rest of it looks :+1: