Allow setting samplerate when reading binary files

Allow setting samplerate when reading binary files

I had a binary file that I needed to decode using UART decoder. UART
decoder needs to know the sample rate for the data, but currently it's
not possible to pass parameters to input formats and so the "binary"
file format always sets the samplerate to 0.

This patch adds the possibility to append a colon-separated list of
key=value options to the -I argument, in the same way -d supports it.
Also, it makes the "binary" format support the "samplerate" option.

I included the GHashTable containing input format options directly in
the sr_input struct. I'm not sure if that's the right way to do it. I
saw that -d uses a much more elaborate system with device capabilities
and typed options, but that seemed like an overkill for input formats.