Add Schedule.playground, have fun!

Schedule.playground/Contents.swift

@@ -0,0 +1,24 @@
+import PlaygroundSupport
+import Schedule
+
+PlaygroundPage.current.needsIndefiniteExecution = true
+
+let t1 = Plan.after(1.second).do {
+    print("1 second passed!")
+}
+
+let t2 = Plan.after(1.minute, repeating: 0.5.seconds).do {
+    print("Ping!")
+}
+
+let t3 = Plan.every("one minute and ten seconds").do {
+    print("One minute and ten seconds have elapsed!")
+}
+
+let t4 = Plan.every(.monday, .tuesday, .wednesday, .thursday, .friday).at(6, 30).do {
+    print("Get up!")
+}
+
+let t5 = Plan.every(.june(14)).at("9:30").do {
+    print("Happy birthday!")
+}

Schedule.playground/contents.xcplayground

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='macos'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Schedule.xcodeproj/project.pbxproj

@@ -72,6 +72,7 @@
 		629FAA702255D14800ED5D67 /* WeekdayTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WeekdayTests.swift; sourceTree = "<group>"; };
 		629FAA722255D1CA00ED5D67 /* PeriodTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PeriodTests.swift; sourceTree = "<group>"; };
 		629FAA742255D6B100ED5D67 /* MonthdayTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MonthdayTests.swift; sourceTree = "<group>"; };
+		66274E9B2258F61800964B93 /* Schedule.playground */ = {isa = PBXFileReference; lastKnownFileType = file.playground; path = Schedule.playground; sourceTree = "<group>"; xcLanguageSpecificationIdentifier = xcode.lang.swift; };
 		OBJ_10 /* Bag.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Bag.swift; sourceTree = "<group>"; };
 		OBJ_13 /* Extensions.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Extensions.swift; sourceTree = "<group>"; };
 		OBJ_14 /* Interval.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Interval.swift; sourceTree = "<group>"; };
@@ -163,6 +164,7 @@
 		OBJ_5 = {
 			isa = PBXGroup;
 			children = (
+				66274E9B2258F61800964B93 /* Schedule.playground */,
 				OBJ_6 /* Package.swift */,
 				OBJ_7 /* Sources */,
 				OBJ_24 /* Tests */,