stlink: new package

stlink is an in-circuit debugging and programming tool for ST-Link v1
and v2 devices. It is similar to OpenOCD but just for ST-Link devices.

  https://github.com/texane/stlink

IMPORTANT: You need permissions to access the stlink usb devices. Here
are example udev rules for stlink v1 and v2 so you don't need to have
root permissions (copied from <stlink>/49-stlink*.rules):

  SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3744", MODE:="0666", SYMLINK+="stlinkv1_%n"
  SUBSYSTEMS=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE:="0666", SYMLINK+="stlinkv2_%n"
Merge pull request #495 from bjornfor/stlink

stlink: new package
Add isPath to trivial.nix

Signed-off-by: Shea Levy <shea@shealevy.com>
Revert "Add isPath to trivial.nix"

This breaks NixOS, and I don't actually need it, so someone who needs it
can bring this back without breaking NixOS :)

This reverts commit 2742087bdd092d77083dc99cdafb6e93444fba3e.

Signed-off-by: Shea Levy <shea@shealevy.com>