INK_SDK_VERSION_5_2 -> TS_SDK_VERSION_2_0

We should clean up the SDK version "registry", since we "promise" to keep this API compatible within the 2.0.x releases. My suggestion is to simply replace INKSDKVersion with this:

typedef enum

{ TS_SDK_VERSION_2_0 = 0, INK_SDK_VERSION_5_2 = 0, }

TSSDKVersion;

(we'd insert TS_SDK_VERSION_2_2, TS_SDK_VERSION_3_0 etc. as we make new "major" releases).