Add async/await API

Sources/SendGridKit/SendGridClient+Concurrency.swift

@@ -0,0 +1,18 @@
+#if compiler(>=5.5) && canImport(_Concurrency)
+
+import NIOCore
+
+@available(macOS 12, iOS 15, watchOS 8, tvOS 15, *)
+extension SendGridClient {
+    public func send(emails: [SendGridEmail]) async throws {
+        let eventLoop = httpClient.eventLoopGroup.next()
+        try await send(emails: emails, on: eventLoop).get()
+    }
+
+    public func send(email: SendGridEmail) async throws {
+        let eventLoop = httpClient.eventLoopGroup.next()
+        try await send(email: email, on: eventLoop).get()
+    }
+}
+
+#endif