Added support for AWS CloudTrail via Aws::CloudTrail.
Aws::Credentials#set? now returns false when populated with empty strings.
Added basic support and integration tests Aws::CloudTrail.

Fixes #53
Rake tasks no longer requires cucumber, only when running integration tests.
Add a Plugin for Shared Access Credentials

Implements the shared access credentials specification, to attempt to
load credentials from the `~/.aws/credentials` file. Supports access
credential profiles as well.
Add Shared Credential Plugin
Minor refactor on SharedCredentials.

Changes:

* Constructor now accepts options hash instead of positional params.
* Removed duplicate after initialize for credentials config option.
* Moved ini parsing from Aws::Util in SharedCredentials.
* Extracted a few methods from SharedCredentials for clarity.
Merged in 'credentials' branch to add support shared credentials.
Moved SharedCredential loading logic into Credentials plugin.
Added support to Aws::SQS for message attributes.
Refeactored the three credential plugins into a CredentialProviderChain.

This will require the API configurations to be rebuilt.
Removed the now-defunkt instance profile credentials plugin.
Updated credential and region coniguration examples in the README.
Bump version to v2.0.0.rc7
Rake tasks no longer requires cucumber, only when running integration tests.
Add a Plugin for Shared Access Credentials

Implements the shared access credentials specification, to attempt to
load credentials from the `~/.aws/credentials` file. Supports access
credential profiles as well.
Add Shared Credential Plugin
Minor refactor on SharedCredentials.

Changes:

* Constructor now accepts options hash instead of positional params.
* Removed duplicate after initialize for credentials config option.
* Moved ini parsing from Aws::Util in SharedCredentials.
* Extracted a few methods from SharedCredentials for clarity.
Moved SharedCredential loading logic into Credentials plugin.
Added support to Aws::SQS for message attributes.