Added support for OS X

- Fixed OS X warning on size_t to uint32_t conversion
- Modified podspec file to support same platforms as AFNetworking

Signed-off-by: Stefan Paychère <stefan.paychere@epyx.ch>
Bumping version to 2.0.1

Since there is a warning fix, updated the version to 2.0.1

Signed-off-by: Stefan Paychère <stefan.paychere@epyx.ch>
Merge pull request #56 from stefanhp/master

Added support for OS X