- rename from "libsndio" to "sndio"
- remove support for "frame tick" synchronization; nothing uses it
- as with many other sndio backends, the audio device block size is the
buffer-write-size the application wants and there are 2 blocks per
device buffer
- if SDL will resample, increase the audio block and buffer size by
the same ratio, so that device latency (or how much *time* the
application has between write()s to not let the buffer underrun) does
not change
- allow applications to disable conversions
tested with almost every port that uses this code (exceptions being some
games that require non-free game data) on a device most likely to be
affected by the changes (azalia(4) that only does 44.1 or 48 kHz s16)
unoverriding conversion disabling exposes brokenness in a few other
ports, those will be fixed soon
