Add spec to show that `AWS2Signature#sign` is correct
Add spec to show that `AWS2Signature#sign` is correct

Using the example in http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAuthentication.html#RESTAuthenticationExamples

StringToSign:

```
GET\n
\n
\n
Tue, 27 Mar 2007 19:36:42 +0000\n
/johnsmith/photos/puppy.jpg
```

Request:

```
GET /photos/puppy.jpg HTTP/1.1
Host: johnsmith.s3.amazonaws.com
Date: Tue, 27 Mar 2007 19:36:42 +0000
Authorization: AWS AKIAIOSFODNN7EXAMPLE:bWq2s1WEIj+Ydj0vQ697zp+IXMU=
```

kevmoo/travis-build,kevmoo/travis-build,craigcitro/travis-build,JuliaCI/travis-build,akoeplinger/travis-build,akoeplinger/travis-build,jhass/travis-build,craigcitro/travis-build,jhass/travis-build,JuliaCI/travis-build,andyli/travis-build,andyli/travis-build