Code generation with preprocessor metaprogramming

[vukics]

Using Boost.Preprocessor for slicing operator to accept any number of arguments. (Cf. #44)

[slayoo]

We need to add checks for Boost to CMakeLists.txt, also .travis.yml and appveyor.yml files need an update to make continuous integration be "green".

And a question that was around for some time - are we OK to make Boost a required dependency or rather an option (like with serialisation and MPI)?

@citibeth @pguio @papadop ?

[vukics]

@slayoo Yes, Boost dependency is an important decision to make.

Also, at present it’s only a proof of principle in this branch, a lot more code repetitions should be replaced with Boost.Preprocessor like this to make it worth adding this dependency.