painful, and not perfect, but at this point the output builds
on a vivid system python2 (bddeb --python2) or python3.
* remove use of cheetah by bddeb in favor of builtin renderer
* add '--python2' flag to bddeb and knowledge of python 2 and python3
package names.
* read-dependencies can now read test-requirements also.
* differenciate from build-requirements and runtime requirements.