In order to be consistent with other services moving to raspberrypi.com,
send telemetry there instead of raspberrypi.org.
Note that the raspberrypi.org endpoint will continue to work
indefinitely in order to support existing clients.
- Use larger buffer size when writing uncompressed files
(was libcurl's default of 16 kb, change it to 128 kb)
- Uncompress the next MB of data, while it is hashing/writing to
disk in seperate thread.
