Upgrade GCC48 to 4.8.3

Merge pull request #6 from boxen/rm-gcc48-3

Update GCC48 version to 4.8.3 and add boxen prefix

2.0.101: Extract apple-gcc42 as its own class

This way you can force installs of apple-gcc42 on mavericks, even if we
don't install it by default

0.0.2

• Fix package hashing because Homebrew

0.0.1

• Add GCC module