Added Swift Programming language book

Recently introduced at WWDC 2014, added official programming language book from Apple

free-programming-books.md

@@ -141,6 +141,7 @@
 * [Smalltalk](#smalltalk)
 * [SQL (implementation agnostic)](#sql-implementation-agnostic)
 * [SQL Server](#sql-server)
+* [Swift](#swift)
 * [Standard ML](#standard-ml)
 * [Subversion](#subversion)
 * [Tcl](#tcl)
@@ -1624,6 +1625,10 @@ See also [TeX](#tex)
 * [Version Control with Subversion](http://svnbook.red-bean.com/)
 
 
+###Swift
+* [The Swift Programming Language](https://itunes.apple.com/us/book/swift-programming-language/id881256329?mt=11) (iBook)
+
+
 ###Tcl
 * [Tcl Programming](http://en.wikibooks.org/wiki/Programming:Tcl), by Richard.Suchenwirth, et. al.
 * [TclWise](http://www.invece.org/tclwise/index.html), by Salvatore Sanfilippo