fix format and samplerate detection using aplay; revert using a variable (pseudo_audio_file) instead of the (buggy!) usage of /dev/zero like in pre-v2 branches

Update README.md reflecting the unfortunate death of lacocina.nl last year, in the respectable age of 18 years. (I'm still somewhat alive though ;) 

- added mute (alactl store/restore) functions to supress sounds when using OPT_SAMPLERATES
- fixed json output

alsa-capabilities.1.md:

- removed CAUTION for using the OPT_SAMPLERATES switch

README.md:

- removed CAUTION for using the OPT_SAMPLERATES switch
- updated json documentation