Added `CRADLE_THROW_WITH_NESTED`.

* test/unit/exception/backtrace_info_run.cpp: Added checks.
* test/unit/exception/throw_exception_run.cpp: Added checks.
* cradle/exception/throw_with_nested.hpp: New. Added
  `CRADLE_THROW_WITH_NESTED`.
* test/unit/exception/throw_with_nested_run.cpp: New. Added a unit test of
  `CRADLE_THROW_WITH_NESTED`.
Merge pull request #11 from Cryolite/feature/throw_with_nested

Added `CRADLE_THROW_WITH_NESTED`.