Execute custom commands from pkg directory
Execute custom commands from pkg directory

E.g., if the following script exists:

    apps/blinky/scripts/run.sh

then `apps/blinky/pkg.yml` can specify:

    pkg.pre_build_cmds:
        scripts/run.sh: 100

apache/incubator-mynewt-newt,apache/incubator-mynewt-newt