Fix run-tests so it looks for "exemplar' in concept exercises.

[rmonnet]

In concept exercises, .meta/config.json use the key "exemplar" for the solution example file while practice exercises look for the key "example". I added some logic in run-test.sh to pick the correct key based on the exercise being tested.

This is preventing PR #81 to pass the GHA tests.

[glennj]

A couple of other things to do:

• add a .files.exemplar to the track config.json (ref the go track)

• modify bin/gen-exercise.sh to tell it whether you're creating a concept or practice exercise -- it's currently hardcoded

  I would do this:

  type=practice
  while getopts :hpca:d: opt; do
      case $opt in
          h) show_help; exit ;;
          p) type=practice ;;
          c) type=concept ;;
          a) author=$OPTARG ;;
          d) difficulty=$OPTARG ;;
          ?) die "unknown option: -$OPTARG" ;;
      esac
  done
  shift $((OPTIND - 1))
  
  exercise_name="${1:-}"
  exercise_path="exercises/${type}/${exercise_name}"
  
  [[ -z $author ]]     && read -rp 'What is your github userid? ' author
  [[ -z $difficulty ]] && read -rp 'What do you guess the difficulty is? ' difficulty
  
  ...
  
  bin/configlet create "--${type}-exercise" "$exercise_name" --author "$author" --difficulty "$difficulty"

  Then we could do:

  bin/gen-exercise.sh -a rmonnet -d 2 -c lasagna

[glennj]

Ah, except that configlet create --concept-exercises doesn't accept --difficulty ... more logic needed there.

[rmonnet]

@glennj , I did update gen-exercise.sh to generate either a practice or concept exercise per your advises. There was a couple of things that configlet create doesn't handle correctly and I got the script to fix these. The tricky part is that there is no problem specification for a concept exercise so the generated files are barebone. I tested on both a practice and a concept exercise and configlet lint was happy with the result.

Take a look and let me know what you think.

[rmonnet]

@glennj, I wanted to change the title of the PR but that doesn't seem possible in github. It contains a revised version of gen-exercise.sh that can generate concept exercises as well as practice exercises.