Removed tests for `cradle/preprocessor`.
Added `cradle::exception::get_num_uncaught_exceptions`.

* jamroot: Added `CRADLE_LINK_PROPERTIES` and `CRADLE_RUN_PROPERTIES`.
* ext/boost/jamfile: Fixed to accept `intro` targets.
* cradle/exception/uncaught_exception.hpp: Newly added.
* src/jamfile: Added dependencies on `boost//headers_compile` and
  `boost//headers_link`.
* src/exception/jamfile: Newly added.
* src/exception/uncaught_exception.cpp: Newly added.
* test/jamfile: Added dependencies on `boost//headers_compile`,
  `boost//unit_test_framework_compile`, `boost//headers_link` and
  `boost//unit_test_framework_link`.
* test/exception/jamfile: Newly added.
* test/exception/uncaught_exception_run.cpp: Newly added.
* doc/.gitignore: Added to ignore `doc/html` directory.
* doc/cradle.xml: Fixed bugs.
* doc/exception/exception.xml: Fixed document for
  `cradle::exceptions::get_num_uncaught_exceptions`.