Remove some of the hardcoded values (the absolute smallest buffer size,
independent on the sample rate) to a config option. Set it to the
default value of 4, like what it was before.
Change the hardcoded absolute lowest limit to 1 because anything else
does not make sense.
Enforce the quantum-floor when calculating the final graph quantum.
Fixes#3908
Pick relevant doc updates.
doc: fix DoxygenLayout.xml for doxygen 1.10
doc: add reference docs + index for config and env variables
doc: add some more coverage
doc: move config man pages under config/
doc: add sections to index, clarify discussion of properties
doc: disable dot graphs in API docs again
doc: some updates
doc: fix up example dependencies in meson
