feat: keep up with ts-fsrs, update algorithm version to 5.0 (#15)

- Delete original source file
- Implemented FSRS 5.0
- Add tests

Package.swift

@@ -1,20 +1,27 @@
-// swift-tools-version: 5.7
+// swift-tools-version: 6.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
 
 import PackageDescription
 
 let package = Package(
-    name: "fsrs",
+    name: "FSRS",
     platforms: [
         .macOS(.v10_13), .iOS(.v14),
     ],
     products: [
-        .library(name: "FSRS", targets: ["FSRS"]),
+        .library(
+            name: "FSRS",
+            targets: ["FSRS"]),
     ],
     targets: [
-      .target(name: "FSRS"),
-      .testTarget(
-        name: "FSRSTests",
-        dependencies: [ "FSRS" ]
-      ),
+        .target(
+            name: "FSRS",
+            path: "Sources/FSRS/"
+        ),
+        .testTarget(
+            name: "FSRSTests",
+            dependencies: ["FSRS"],
+            path: "./Tests/FSRSTests"
+        ),
     ]
 )