add coccinelle worker

Located in ethel/[wrappers|runners|commands]/coccinelle.py,
it adds the possibility to run coccinelle static tool on C files.
add executable for downloading/updating a folder of firehose-oriented semantic patches
fix: remove hard coded config file
fix: remove __main__ (used for tests)
move coccinelle installation instructions to PACKAGING
Merge pull request #3 from matthieucan/coccinelle

Coccinelle