Remove the `_pinkerton` function.

Make `\Phuedx\Pinkerton\Pinkerton::spyOn` and `::stopSpyingOn` static.
Remove `\Phuedx\Pinkerton\Pinkerton` private helper methods.

Initially, `\Phuedx\Pinkerton\Pinkerton::spyOn` was intended to spy on
both functions and methods. This was made explicit by - prematurely -
refactoring the body of the `::spyOn` method into the `::spyOnFunction`
method. Since Pinkerton only focusses on spying on functions, this
refactoring has been undone.
Add the `createSpy` function.

Alter `Spy#__construct` so that it doesn't require a callable.
Remove the redundant src/spec/bootstrap.php file.
Add the “Testin’” section.
Make the dependency on the runkit extension explicit.
Add the `Spy#andReturn` method.
Build against PHP versions ~5.4 and ~5.5.
Move src/main to main and src/spec/ to spec/
Move spec/ to test/
Convert Spy PHPSpec spec to PHPUnit unit test
Convert Pinkerton PHPSpec spec to PHPUnit unit test
Make Travis CI run the PHPUnit tests
Remove the PHPSpec dependency
Migrate Pinkerton class from runkit to UOPZ

* Rewrite Pinkerton::spyOn and Pinkerton::stopSpyingOn to use
  uopz_function and uopz_restore respectively
* Remove the Pinkerton::getSpy function as the UOPZ handler closes over
  the spy
Depend on ext-uopz and not ext-runkit
Install ext-uopz during the Travis CI build
Office Clerical

* Bump copyright year
* Add my hip to the groove email address
* Update description field in package.json
Merge branch 'develop'