VID/PID based device type detection

[bridadan]

This builds on #369 to solve issue #165.

In PR #299 I added device type detection. It used a strategy that made use of the files present on the device to identify which firmware was most likely running on the interface chip. This was good enough to differentiate between JLink and DAPLink based firmwares, but got a little more complicated for firmwares like ST-Link. ST-Link tends to mimic DAPLink files quite closely, so this option isn't really feasible any more.

This PR switches the strategy to instead identify device types by the Vendor ID. In this case I'm not currently using the Product ID as it does not seem necessary at this point. There also is a small chance that the Product IDs may vary a bit depending on the release of the interface firmware, so I figured I'd postpone this change until we have evidence to the contrary.

Details to review (please 😄)

This also adds stlink to the list detectable firmwares. The STLink detection makes use of the DAPLink update logic at the moment, meaning you will see daplink_build and daplink_version in the JSON output, even though this is using stlink. I did this on purpose because this is how the information would have showed up in earlier versions. Should I also provide this info as stlink_*? Should I leave it how it is?

FYI @jupe @theotherjimmy

[coveralls]

Coverage increased (+0.02%) to 80.462% when pulling b0aa4be on bridadan:firmware_detection into 281c44a on ARMmbed:master.

[theotherjimmy]

I'm fine with it as it is @jupe?

[jupe]

Can we rely on to these thtee VID in every boards now? what happens if VID does not match to some?

[bridadan]

Yes I believe we can, especially on anything released within the past few years. If the VID does not match it will default to the 'daplink' style detection (just like it used to).