Add VersionProvider

Sources/ElixxirDAppsSDK/VersionProvider.swift

+import Bindings
+
+public struct VersionProvider {
+  public var get: () -> String
+
+  public func callAsFunction() -> String {
+    get()
+  }
+}
+
+extension VersionProvider {
+  public static let live = VersionProvider(get: BindingsGetVersion)
+}
+
+#if DEBUG
+extension VersionProvider {
+  public static let failing = VersionProvider { fatalError("Not implemented") }
+}
+#endif