Add toolchain directory with cmake toolchain files used to find
compilers and set C++ versions

The following configurations are build on Windows using appveyor
service:
- enable MSVC 2015 SDK 8.1
- enable MSVC 2015
- enable MSVC 2017
- enable MSVC 2017 c++17
- enable mingw-cxx11
- enable mingw-gnuxx11
- enable mingw-cxx17

The following configurations are build on Linux using travis service:
- enable Ubuntu 14.04 amd64/i386, C++11
- enable Ubuntu 16.04 amd64/i386, C++11
- enable Ubuntu 18.04 amd64 C++98, C++11, GNU++11, C++17
- enable mingw-w64 on Ubuntu 18.04 amd64, C++11, GNU++11, C++17

The tests for cross compiled mingw windows binaries are run using wine64