Fix XCode error caused by non-unique file names

Swift seems to require files within a module to have unique names. It uses the file names to disambiguate private methods.
Remove Optional:Printable extension for Swift 1.1

It is no longer legal to add public methods to a type defined in another module, according to the error message.
Update tests to compile in XCode 6.1

Tests currently fail due to the removal of the Optional:Printable extension.
Fix output of matched values when tests fail.

A previous commit removed the Printable extension on Optional types, since XCode 6.1/Swift 1.1 does not allow external types to have public extensions.

That extension made output of optionals clearer, and this commit restores that functionalityl.
Remove Nimble.playground

Nimble.playground contained no relevant content.
Merge pull request #35 from nerdyc/xcode61-beta2

Updates to support Xcode 6.1 Beta 2
Merge pull request #38 from modocache/remove-playground

Remove Nimble.playground