Add out-of-the-box support for date formats used by HTTP/1.1

Adds support for RFC 1123, RFC 850, and ANSI C asctime() date formats
Details: http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.3.1
Add test cases for new date formats
Add formats to README.md
Switch to xcpretty
Merge branch 'sadlerjw-http-date-formats'
Switch to XCTest
Update to Expecta 0.3.0
Bump Podspec version to 1.1.0