Buffered squelch
The idea is to pass samples through a delay line so that the exact squelch open and close times can be optimized to match the actual transmission. See here: https://brmlab.cz/user/jenda/kukuruku ("Squelch sucks").
Applied to NFM and AM demods. Most significant improvement is with the suppression of squelch noise tail in the NFM demod. This has been improved too in the SSB demod.
Applied to DSD demod also to help catch the very beginning of transmission regardless of gate time which is important for digital transmissions.
Other changes
Merged contributions of jigpu (thanks!) to fix memory issues and spelling errors in documentation.