Kata: StringCalculator in C++ step by step using GoogleMock and Boost.Regex

I've just coded the StringCalculator kata in C++ using GoogleMock and Boost.Regex.

I commited it step by step. Check the resulting code in Github.

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Update:
I did some refactorings to my solution in order to a) reduce some duplication and b) avoid having to use Boost.Regex.
They're explained, respectively, in the two following posts:

• Extracting reusable C++ templated functions from StringCalculator code
• Using C++11 to split strings without using the boost library