Release v0.15.0

* [ENHANCEMENT] Add 1kB and 2kB units #915
* [BUGFIX] Add error log when probe collector creation fails #918
* [BUGFIX] Fix test build failures on 32-bit arch #919
* [BUGFIX] Adjust collector to use separate connection per scrape #936

Signed-off-by: SuperQ <superq@gmail.com>