Add Fetchcode support for cocoapods #177

CocoaPods doesn’t provide direct download URLs for packages.
Each PURL points to a Git repo and a tag, not a tarball or hosted binary.
To fetch the source, we must parse the podspec, extract the Git URL and tag.

But there is no standardize way to get a Podspec URL

https://cdn.cocoapods.org/all_pods_versions_1_0_0.txt
https://cdn.cocoapods.org/all_pods_versions_2_0_0.txt