add amazon s3 download links
show an single example usage of each of the graphics apis, add download links for stable
fix #33
close #20
Update mac binary link
Add in instructions for PPA for Ubuntu
Merge pull request #36 from staticfloat/jn

Update OSX links, and include instructions for Ubuntu PPA
Add in instructions for PPA for Ubuntu
Fix ubuntu install instructions
Merge pull request #34 from JuliaLang/jn

amazon s3 download links and other fixes