Added Tasks for publishing items with Custom Headers (e.g. for setting etags or gzip headers). Usage Example:

  <ItemGroup>
    <Directories Include="css;scripts;">
	<Content-Type>text/css</Content-Type>
	<Content-Encoding>gzip</Content-Encoding>
    </Directories>
  </ItemGroup>

    <PublishFolderWithHeaders
        Key= "(Key)"
        Secret= "(Secret)"
        SourceFolders = @(Directories)
        Bucket="$(Bucket)"
        DestinationFolder="$(DestinationFolder)" />
Update targets and readme
optimise getting of custom metadata by using CloneCustomMetadata,

- fix error where headers where not propagating into recursion
Test for the amazon S3 DoesS3BucketExist - unclosed web response error.
Updated to Amazon's patched AWSSDK v 1.5.21.0
Merge pull request #3 from cankoluman/dev/ck-1_add_custom_headers

Dev/ck 1 add custom headers