Built-in file processor for binary BEAST format

[denzen84]

Hi all!

Almost a year ago I released beastblackbox utility to process binary BEAST logs.

Today I finished module for dump1090-fa that releases processing for binary BEAST files using standard interface for different types of SDR readers.

I tried to strictly follow the ideology and structure when writing this module. All changes made to neighboring modules (dump1090.h, sdr.c, net_io.c, net_io.h) were forced and did not changes the data processing code. The changes concerned only scope of visibility for certain functions.

Also I note changes in the net_io.c module. I separated the code responsible for generating output in the SBS format as a standalone function. So that this function could be used from other modules.

I hope you found this commit useful.

[mutability]

I'm in two minds about this. This has several things going on, not all of which I want to take:

1. some extra utility options e.g. SBS output to stdout
2. some general changes e.g. the switch-vs-if thing
3. the beast-format input thing

I'd like to see (1) and (2) as separate PRs. Some of the extra options I'm not sure even belong in dump1090; ideally I'd like to stop bolting on new options to dump1090 and have some separate utilities if you want to do things like e.g. ICAO filtering. (this is not a trivial thing to do, I admit).

Re performance, I will generally resist changes to make it "faster" at the expense of clarity unless you can demonstrate a non-trivial improvement, which mostly means changes in the demodulator and almost nowhere else; message decoding is super cheap compared to demodulation.

For (3) I really don't like the current implementation that bolts it on to the SDR logic; that's really the wrong place for it as you're entirely bypassing the demodulator in this case. It should be a separate input mechanism along the lines of network input.

[mutability]

I don't think I can merge this as-is.