Adding podspec pointing to 1.x

With this, CocoaPods users would be able to target `1.x` in their Podfile with the following line:

    pod 'SVGKit', :git => 'https://github.com/SVGKit/SVGKit.git'

However, 1.x in it's current state does't compile with the current podspec.  An example project (with SVGKit already added) can be found here: <https://github.com/pyro2927/SVGKitPodExample>.