Add CLI app support

[tiagolascasas]

Allow the package to be called using a CLI, like this:

clava-etg -i edgedetect.cpp -o edgedetect --apply-transforms --generate-etg

[lm-sousa]

You can use the bin field in the package.json file to achieve that.
See the one in Clava and/or Lara for a couple of examples.