Working through issues with HTTR 0.3 - auth currently returning an error.

Auth currently returning: Response
[https://api2.omniture.com/admin/1.4/rest/?method=Report.Validate]
  Status: 400
  Content-type: application/json
{"error":"Bad Request","error_description":"Invalid created timestamp
(''). Values should be in ISO-8601 format","error_uri":null}
Changed from parsed to text for content() calls, fixed legacy auth build headers method for HTTR 0.3.
Updated minimum version numbers in README.md.
Merge pull request #57 from randyzwitch/version_1_4_content_fixes

Version 1 4 content fixes