This changes the on disk format for new raw reports to be gzip
compressed. Also adds the ability to serve these reports in plain text,
to insulate web browsers from the change (previously we just served the
raw reports from disk using Caddy).
* lib/ur: Implement crash (panic) reporting (fixes#959)
This implements a simple crash reporting method. It piggybacks on the
panic log files created by the monitor process, picking these up and
uploading them from the usage reporting routine.
A new config value points to the crash receiver base URL, which defaults
to "https://crash.syncthing.net/newcrash" (following the pattern of
"https://data.syncthing.net/newdata" for usage reports, but allowing us
to separate the service as required).
