Add 'gcc' cookbook

This cookbook currently provides two recipes:
 - default.rb, to install ubuntu 'gcc' default package
 - ppa.rb, to install latest 'gcc' from ubuntu-toolchain-r/test PPA

Address travis-ci/travis-ci#1379
Related to travis-ci/travis-ci#979
Merge pull request #215 from gildegoma/gcc-4.8

Add 'gcc' cookbook to install gcc 4.8 on ubuntu 12.04LTS