Adding #define of SSZipArchive header inclusion to allow for conditional compilation of libraries which can add functionality conditionally, if SSZipArchive is present.

Signed-off-by: Levi Brown <levi@grokers.net>
Fixed podspec.

Signed-off-by: Levi Brown <levi@grokers.net>
Merge pull request #43 from levigroker/master

#define added to the .h which allows conditional compilation for third parties wishing to conditionally add functionality based on the presence of SSZipArchive.