Add caching of device names/descriptions as parsed from dmesg

[morgant]

Currently, audio device names/descriptions are parsed from the dmesg output every time that xsndiomenu is executed. It would preferable if the device name/description mapping was stored and/or cached on disk the be more quickly retrieved when building the xsndiomenu menu options. Part of the reason for this is that dmesg only keeps a set number of output lines and so if a lot of kernel/device changes happen, it's possible for early device logs to no longer be available.

I'm thinking that the daemon (maybe xsndiomenud?) would first parse dmesg, then tail /var/log/messages and parse new lines for audio device changes. Maybe it would save device names to /var/run/xsndiomenud/ for /var/db/xsndiomenud/, which would give xsndiomenu a consistent location to fetch device names without further parsing.

Another alternative to tailing /var/log/messages would be using hotplugd(8), but would require further configuration by the user.