Add macOS support (#23)

* Add macOS support

* Update README

* Update to v0.2.0

* Document breaking changes

* Delete widget tests

darwin/Classes/Store/NearbyDevicesStore.swift

@@ -0,0 +1,59 @@
+//
+//  NearbyDevicesStore.swift
+//  nearby_service
+//
+//  Created by Kseniia Nikitina on 16/1/24.
+//
+
+import Foundation
+import MultipeerConnectivity
+
+class NearbyDevicesStore : NSObject {
+    static let instance = NearbyDevicesStore()
+    
+    private var devices : [NearbyDevice] = []
+    
+    func getDevices() -> [NearbyDevice] {
+        return devices
+    }
+    
+    func find(for deviceId: String) -> NearbyDevice? {
+        return devices.first { device in
+            return device.peerID.displayName == deviceId
+        }
+    }
+
+    
+    func add(for peerID: MCPeerID, discoveryInfo: [String: String]? = nil) -> NearbyDevice? {
+        devices = devices.filter{$0.peerID.displayName != peerID.displayName}
+        
+        let device = NearbyDevice.fromDictionary(for: discoveryInfo, with: peerID)
+        self.devices.append(device)
+        
+        return device
+    }
+    
+    func remove(for peerID: MCPeerID) {
+        self.devices = devices.filter{$0.peerID.displayName != peerID.displayName}
+    }
+    
+    func clear() {
+        self.devices = []
+    }
+    
+    func toDartFormat() -> String {
+        let devicesObject = devices.map { device in
+            return device.toDictionary()
+        }
+        do {
+            let jsonData = try JSONSerialization.data(withJSONObject: devicesObject)
+            if let jsonString = String(data: jsonData, encoding: .utf8) {
+                return jsonString
+            }
+        } catch {
+            return "[]"
+        }
+        return "[]"
+    }
+    
+}