Make it easier to use jq with shebangs (fix #1044)

Make it easier to use jq with shebangs (fix #1044)

Allow a continuation on a comment immediately after a shebang to make
this traditional hack possible:

    #!/bin/sh
    # this next line is ignored by jq \
    exec jq -f "$0" "$@"
    # jq code follows

But continue only on the first line following a shebang, and only if
it's a comment.