src/wscript_build: move jack to examples

Signed-off-by: Paul Brossier <piem@piem.org>
src/wscript_build: added missing -lm

Signed-off-by: Paul Brossier <piem@piem.org>
python/demos/demo_bpm_extract.py: make executable

Signed-off-by: Paul Brossier <piem@piem.org>
python/ext/py-source.c: not generated, modified init to get samplerate from aubio_source_t

Signed-off-by: Paul Brossier <piem@piem.org>