Change Log:
* CMake dependency bumped to 3.10.
* Moved to target-oriented CMake set-up.
* ExSeisDat can be included in a project via add_subdirectory.
* Compiled/installed ExSeisDat can be used with find_package from the
  ExSeisDat build directory or install directory.
* FFTW3 and MPI now linked as imported targets.
* Added options to enable/disable specific tests
* Added CMake option to add development flags used by the CI environment
  for GCC and Clang.