Added S3 as a deployment artifact source using credentials in data_bags, ENV variables or IAM Instance Roles on EC2
Fixed bucket and object existence checks and related rspec tests, stopped windows from trying to install libxml/libxslt
Added another S3 reference in README.md
Fixed dependencies for aws-sdk (added gcc/make, changed action) and renamed config_for method
Refactored the from_<source>? methods to make them actually return a Boolean (as their docs stated) and added spec tests.  Also removed duplicated methods in the LWRPs
Fixed spacing on README.md and missed from_s3? from refactoring
Removed duplicated text
Merge pull request #71 from jonathanq/s3-artifact-deploy

Amazon S3 as an artifact deployment source