Swift 3.0 Support

[colemancda]

It would be helpful to migrate this to Swift 3.0. I'm trying on my fork, but I don't know all the implementation details.

[lorentey]

@colemancda has contributed support for prerelease versions of Swift 3 on the swift3 branch.

The following subtasks still need to be done before the first Deque (pre)release for Swift 3:

• The package's unit tests need to be updated
• .travis.yml needs to be changed to build the package using Swift 3

[lorentey]

I updated the package to compile on the latest Swift 3 builds (dated 2016-05-31), and fixed the unit tests.
I haven't fixed the Travis setup yet; I think I'll wait for the WWDC build with that.