Codify plugin versioning through the system (#121)

Co-authored-by: Brandon Sneed <[email protected]>

Author: bsneed

Sources/Segment/Plugins.swift

@@ -58,6 +58,10 @@ public protocol DestinationPlugin: EventPlugin {
 
 public protocol UtilityPlugin: EventPlugin { }
 
+public protocol VersionedPlugin {
+    static func version() -> String
+}
+
 // For internal platform-specific bits
 internal protocol PlatformPlugin: Plugin { }
 

Sources/Segment/Plugins/SegmentDestination.swift

@@ -211,3 +211,11 @@ extension SegmentDestination {
         }
     }
 }
+
+// MARK: Versioning
+
+extension SegmentDestination: VersionedPlugin {
+    public static func version() -> String {
+        return __segment_version
+    }
+}