plus some cleanup here and there

as special events.

If we store all received events to a file, this dump is now
self-contained. Helps to analyze traces.

Some functions have also been factorized in the process, too much
duplication.

(Also tracer/Makefile was forgotten in previous commit, included
in this one...)

- add on/off command line options

only works for 5MHz (7680 samples per TTI), one transport block
(basic FDD thing)