Add cmake code to create library for c++

[andreadelprete]

Moreover, add missing include in src/stack-template.t.cpp

[coveralls]

Coverage remained the same when pulling 08632d3 on andreadelprete:master into 51a55f0 on stack-of-tasks:master.

[olivier-stasse]

Could you elaborate a bit on your targeted application ?
Unless you want to move to a pure C++ implementation I am not sure to fully understand
the purpose of putting everything in one library.
Currently the fine granularity allows to avoid unnecessary binary dependencies.
Thanks to the huge work of Florent and Thomas, this is almost not noticeable in python.
So, I would like to fully understand your point of view before introducing a new linking system
likely to add noise in the comprehension of the overall system.

Best,
Olivier.

[andreadelprete]

As you already guessed, I'd like to move to a pure C++ implementation. I find it much easier to reverse-engineer pure C++ code than a mix of C++ and python.