Add async/await support (#15)

* Add async/await support

* Check for compiler version

Author: grdsdev

Package.swift

@@ -5,6 +5,7 @@ import PackageDescription
 
 let package = Package(
     name: "PostgREST",
+    platforms: [.iOS(.v11), .macOS(.v10_10)],
     products: [
         // Products define the executables and libraries a package produces, and make them visible to other packages.
         .library(

Sources/PostgREST/Concurrency.swift

@@ -0,0 +1,14 @@
+import Foundation
+
+#if compiler(>=5.5)
+@available(iOS 15.0.0, macOS 12.0.0, *)
+extension PostgrestBuilder {
+  public func execute(head: Bool = false, count: CountOption? = nil) async throws -> PostgrestResponse {
+    try await withCheckedThrowingContinuation { continuation in
+      self.execute(head: head, count: count) { result in
+        continuation.resume(with: result)
+      }
+    }
+  }
+}
+#endif