Refactored Travis integration and added new targets
Refactored Travis integration and added new targets

List of enabled targets:
On Linux:
+ gcc {4.7, 4.8, 4.9, 5.0, 6.0, 7.0} (without compat tests)
+ gcc 5.0 with compat tests enabled
+ clang {3.5, 3.6, 3.7, 3.8, 3.9, 4.0} (with libsdtc++)

On OSX:
+ XCode {7.3, 8, 8.2, 8.3, 9.0}

Missin Ones:
+ XCode 8.1 (Doesn't have CMake)
+ Linux Clang with libc++ (missing cxxabi.h)
+ Linux Clang 5.0 (missing <type_traits>)

abutcher-gh/cereal,USCiLab/cereal,abutcher-gh/cereal,USCiLab/cereal