input/stf: introduce support for Asix' Sigma Test File format

Introduce the 'stf' input module which interprets *.stf captures
which are the Asix Sigma vendor software's native format. This
implementation supports Sigma Test Files, but does not support
Omega Test Files because ZIP archive handling is not available
in sigrok input modules. This implementation depends on miniLZO.

The input module was tested with vendor provided example captures.
Automatic file format detection, GUI initiated file re-read, and
50MHz as well as 200MHz captures were tested, and successfully
decode I2C, UART, and USB traffic. The trigger position works
(when the file content is plausible, the USB dump was not).