[AltServer] Moves core ConnectionManager logic to AltKit

Refactors ConnectionManager to use arbitrary RequestHandlers and ConnectionHandlers. This allows the core AltServer request logic to be shared across different targets with different connection types.

AltKit/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")
+        }
+    }
+}