add macOS playground

Playground_macOS.playground/Contents.swift

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+import AppKit
+import CoreStore
+
+/// Model Declaration =====
+class Animal: CoreStoreObject {
+    let species = Value.Required<String>("species", initial: "Swift")
+    let master = Relationship.ToOne<Person>("master")
+    let color = Transformable.Optional<NSColor>("color", initial: .orange)
+}
+
+class Person: CoreStoreObject {
+    let name = Value.Optional<String>("name")
+    let pets = Relationship.ToManyUnordered<Animal>("pets", inverse: { $0.master })
+}
+/// =======================
+
+/// Stack setup ===========
+let dataStack = DataStack(
+    CoreStoreSchema(
+        modelVersion: "V1",
+        entities: [
+            Entity<Animal>("Animal"),
+            Entity<Person>("Person")
+        ]
+    )
+)
+try dataStack.addStorageAndWait(SQLiteStore(fileName: "data.sqlite"))
+/// =======================
+
+/// Transactions ==========
+try dataStack.perform(
+    synchronous: { transaction in
+
+        let animal = transaction.create(Into<Animal>())
+        animal.species .= "Sparrow"
+        animal.color .= .yellow
+
+        let person = transaction.create(Into<Person>())
+        person.name .= "John"
+        person.pets.value.insert(animal)
+}
+)
+/// =======================
+
+/// Accessing Objects =====
+let bird = try dataStack.fetchOne(From<Animal>().where(\.species == "Sparrow"))!
+print(bird.species.value)
+print(bird.color.value as Any)
+print(bird)
+
+let owner = bird.master.value!
+print(owner.name.value as Any)
+print(owner.pets.count)
+print(owner)
+/// =======================

Playground_macOS.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos' executeOnSourceChanges='false'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Playground_macOS.playground/playground.xcworkspace/contents.xcworkspacedata

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+<?xml version="1.0" encoding="UTF-8"?>
+<Workspace
+   version = "1.0">
+   <FileRef
+      location = "self:">
+   </FileRef>
+</Workspace>

Playground_macOS.playground/playground.xcworkspace/xcshareddata/IDEWorkspaceChecks.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>IDEDidComputeMac32BitWarning</key>
+	<true/>
+</dict>
+</plist>