In all causes of action, suits, matters or proceedings brought for the enforcement of any note, bond, mechanics lien, mortgage, invoice or other instrument of writing, if the plaintiff or lien holder in the action, suit or proceeding recovers judgment in any sum, the plaintiff or lien holder may also recover reasonable counsel fees, which shall be entered as a part of the judgment in the action, suit or proceeding. Such counsel fees shall not in any such action, suit or proceeding, exceed 20 percent of the amount adjudged for principal and interest. Such counsel fees shall not be entered as a part of such judgment unless the note, bond, mortgage, invoice or other instrument of writing sued upon, by the terms thereof, expressly provides for the payment and allowance thereof, except in the cases of mechanic's liens in which no express agreement shall be necessary in order to entitle the lien holder to reasonable counsel fees.