IncrementsComboOneDrugOnly is the class for increments control in combination
trials when only one drug is allowed to be escalated.
Details
Under this rule, when escalating drug 1 to a dose above the last administered drug 1 dose, drug 2 must remain at or below its last administered dose, and vice versa. In other words, at most one drug may be escalated in any given cohort. No parameters are required; the rule is fully defined by the "one drug only" principle.
