Update to v0.12.1

Based on https://github.com/Blufe/chef-wkhtmltopdf
consistent node attribute access
Spec for binary recipe
Spec source recipe
cache chef_run
Add kitchen config
Fix ubuntu trusty package dependencies
Add serverspec integration tests
Add source recipe
Add centos7 and fix rpm dependencies
Fix rhel dependency_packages
Use more rspec3 syntax
fix setting download url for source
Correct extracted path of source tarball
Use build script
spec for source install
Use installers from local package
Remove integration tests for Ubuntu 12.10 as no longer supported by Canonical
Fix static build path
patch build script for 0.12.1