Ability to add Variables to Contracts

Variable Tags such as:

%first_name%, %last_name%, %rental_spaces%, %rental_start_datetime%, %rental_end_datetime%, %rental_deposit%, %rental_deposit_due_date%, %rental_total%, %rental_total_due_date%, %group_name%, %group_email%, %group_phone%, %group_address%, %group_city%, %group_state%, %group_zip%