[AltKit] Replaces dedicated AltKit module with shared files across targets

Treating AltKit as a full module resulted in more complexity than necessary, when we really just wanted to share some files between different targets. Now we can share individual files across modules as-needed without AltKit overhead.

Shared/Extensions/Result+Conveniences.swift

@@ -0,0 +1,76 @@
+//
+//  Result+Conveniences.swift
+//  AltStore
+//
+//  Created by Riley Testut on 5/22/19.
+//  Copyright © 2019 Riley Testut. All rights reserved.
+//
+
+import Foundation
+
+public extension Result
+{
+    var value: Success? {
+        switch self
+        {
+        case .success(let value): return value
+        case .failure: return nil
+        }
+    }
+    
+    var error: Failure? {
+        switch self
+        {
+        case .success: return nil
+        case .failure(let error): return error
+        }
+    }
+    
+    init(_ value: Success?, _ error: Failure?)
+    {
+        switch (value, error)
+        {
+        case (let value?, _): self = .success(value)
+        case (_, let error?): self = .failure(error)
+        case (nil, nil): preconditionFailure("Either value or error must be non-nil")
+        }
+    }
+}
+
+public extension Result where Success == Void
+{
+    init(_ success: Bool, _ error: Failure?)
+    {
+        if success
+        {
+            self = .success(())
+        }
+        else if let error = error
+        {
+            self = .failure(error)
+        }
+        else
+        {
+            preconditionFailure("Error must be non-nil if success is false")
+        }
+    }
+}
+
+public extension Result
+{
+    init<T, U>(_ values: (T?, U?), _ error: Failure?) where Success == (T, U)
+    {
+        if let value1 = values.0, let value2 = values.1
+        {
+            self = .success((value1, value2))
+        }
+        else if let error = error
+        {
+            self = .failure(error)
+        }
+        else
+        {
+            preconditionFailure("Error must be non-nil if either provided values are nil")
+        }
+    }
+}