[Feature] Some basic core feature (#1)

This PR refers to the work done on setting the `Core` target as well as implemented some basic features as extension to a pair of `Swift` primitive types.

To give further details about this work:
- [x] defined the `Core` target;
- [x] implemented the **empty** static property and the **isNotEmpty()** function in the `String+Empty` extension;
- [x] implemented the **init(_: )** initialiser fo strings in the `Bool+Init` extension;

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #1

Sources/Core/Extensions/Bool+Init.swift

@@ -0,0 +1,37 @@
+//
+//  Bool+Init.swift
+//  Core
+//
+//  Created by Javier Cicchelli on 15/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+public extension Bool {
+    
+    // MARK: Initialisers
+
+    /// Initialise a boolean primitive out of a given string.
+    /// - Parameter string: A string to initialise the boolean with.
+    init(_ string: String) {
+        let strings: [String] = [
+            .Constants.oneNumber,
+            .Constants.oneWord,
+            .Constants.true,
+            .Constants.yes
+        ]
+        
+        self = strings.contains(string.lowercased())
+    }
+    
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    enum Constants {
+        static let yes = "yes"
+        static let `true` = "true"
+        static let oneWord = "one"
+        static let oneNumber = "1"
+    }
+}

Sources/Core/Extensions/String+Empty.swift

@@ -0,0 +1,24 @@
+//
+//  String+Empty.swift
+//  Core
+//
+//  Created by Javier Cicchelli on 15/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+public extension String {
+    
+    // MARK: Properties
+    
+    /// Represents an empty string.
+    static let empty = ""
+    
+    // MARK: Functions
+    
+    /// Checks whether a string is not empty.
+    /// - Returns: A boolean value that represents whether the string is not empty.
+    func isNotEmpty() -> Bool {
+        isEmpty == false
+    }
+    
+}