Update 13th_Age.html

Added in Backgrounds
Update 13th_Age.css

added sheet-hit css field
Update 13th_Age.html

added in place holders for most of the remaining sections and added in Basic Hit field
Finished

Completely functional except for the bugs I assume are from the roll20 side with calculating attributes and repeating sections. Not very pretty but I will leave that to people who actually know this sort of thing.
Update todo
Merge pull request #18 from Twibbit/master

Ready for actual use