call to get returns response headers
Merge pull request #1 from palmerabollo/feature/get_returns_headers

Call to get returns response headers
store the headers in cache. Return headers only when there was any response.
Merge pull request #2 from anabelengp/feature/get_returns_headers_with_cache

Store the headers in cache. Return headers only when there was any res.
Merge pull request #31 from palmerabollo/v6.5

Make response headers available when calling "_get"