added the --pyrex-debug flag to Cython's build_ext
added the pyrex_debug boolean to Cython's Cython.Distutils.extension.Extension
    (for per-module debugging information)
debug output is written to the cython_debug directory
bin/cygdb is included (start this from the build directory)
    working commands: cy import, cy locals, cy break
when debugging is active, export all functions as extern