Support reading from stdin and report syntax errors.
Also don't do extra spa_json_enter when inserting a dummy "{" when
parsing files with top-level keys. In this case the tokenizer is
already "entered" after spa_json_init, and will give parse error when we
are not inserting the closing "}" for the dummy "{".
Fix some copypaste mistakes and other errors.
Add explanations for some more properties. Explain "drop-in" config
files. Explain filter-chain.conf.
Move configuration man pages under Configuration in TOC.
Add reference documentation for configuration settings & node/device
properties. We should have boring & exhaustive reference lists of all
the options, and an index where they can be looked up as needed.
The content is mostly stolen from the Wiki.
Add pipewire-client.conf.5, pipewire-jack.conf.5, and pipewire-device.7
that try to explain all available configuration settings for native/ALSA/JACK
clients, and parameters & properties devices.
Expand pipewire.conf.5 and pipewire-pulse.conf.5 with lists of supported
properties. Also explain environment variables.
Doxygen doesn't have an indexing mechanism suitable for configuration
settings, so add a simple one using an input filter and use it here.
Tweak styling a bit.
Use (fixed-up) Doxygen manpage output for all program & module manpages.
This also allows formatting the manual pages properly in the HTML docs.
The Markdown pages work properly only with Doxygen >= 1.9.7, older
versions put them to wrong place in the HTML docs.
