Tweaked version constraints
Merge pull request #361 from GrahamCampbell/patch-2

Tweaked Version Constraints
Reducing the number of signed sigv4 headers.

This commit is similar to https://github.com/aws/aws-sdk-php/pull/364.
Merge pull request #365 from aws/v2_signature_headers

Reducing the number of signed sigv4 headers (for v2)
Prepping the 2.7.1 release
Updated UPGRADING guide with a brief blurb about version 2.7
Automating github API releases for v2
Removing regions list from doc output, and instead using rande.html
Fixed #369. Corrects the HashUtils::hexToBin function for PHP 5.3 users.
Fixed #373. Corrects a date formatting issue in CognitoSyncClient::updateRecords.
Adding support for config driven endpoints

Added an "endpoint_provider" config option.
Added eu-central-1 as a v4 only S3 region.
Update IAM
Updating Amazon Cognito Identity
Updating Amazon Route 53 domains
Updating Amazon EC2
Updating Amazon ElastiCache
2.7.2 release
chdir properly to parent directory
Ensuring content-md5 is signed
Updating to work with the latest version of chag