Add no-doctest to exclude .rst files from doctest processing

    if [ -z "$NO_DOCTESTS" ]; then

      RST_FILES=(../doc/*.rst)

      if [ -e "${RST_FILES[0]}" ]; then

        TESTABLES="$TESTABLES ${RST_FILES[*]}"

      for f in "${RST_FILES[@]}"; do

        if [ -e "$f}" ]; then

          if ! grep -q no-doctest "$f"; then

            TESTABLES="$TESTABLES $f"

          fi

        fi

      done

      # macOS bash is too old for mapfile: Oh well, no doctests on mac.

      if [ "$(uname)" != "Darwin" ]; then