Adds autodetection of ContentType for AwsS3 adapter.
Makes content-type detection configurable when adapter is instantiated.
Adds description to composer.json about how the suggested ext-fileinfo extension is used.
Defaults content-type detection to false in AwsS3 adapter to prevent breaking existing usage.
Merge pull request #236 from woodsae/awss3-automatic-content-type-detection

AwsS3 Automatic Content-Type Detection