Add CHANGELOG.md entries for SE-0110 and SE-0148

Author: slavapestov

CHANGELOG.md

@@ -6,6 +6,7 @@ CHANGELOG
 
 | Contents               |
 | :--------------------- |
+| [Swift 4.0](#swift-40) |
 | [Swift 3.1](#swift-31) |
 | [Swift 3.0](#swift-30) |
 | [Swift 2.2](#swift-22) |
@@ -17,6 +18,28 @@ CHANGELOG
 
 </details>
 
+Swift 4.0
+---------
+
+* [SE-0148][]:
+
+  Subscript declarations can now be defined to have generic parameter lists.
+  Example:
+
+  ```
+  extension JSON {
+    subscript<T>(key: String) -> T?
+        where T : JSONConvertible {
+      // ...
+    }
+  }
+  ```
+
+* [SE-0110][]:
+
+  In Swift 4 mode, Swift's type system properly distinguishes between functions that
+  take one tuple argument, and functions that take multiple arguments.
+
 * More types of C macros which define integer constants are supported by the
   importer. Specifically the `+, -, *, /, ^, >>, ==, <, <=, >, >=` operators
   are now recognized, and the previously-supported `<<, &&, ||, &, |`