Converts this stub convention to the appropriate roll convention.
This converts a stub convention to a
RollConvention based on the
start date, end date, frequency and preference for end-of-month.
The net result is to imply the roll convention from the schedule data.
The rules are as follows:
If the input frequency is month-based, then the implied convention is based on
the day-of-month of the initial date, where the initial date is the start date
if rolling forwards or the end date otherwise.
If that date is on the 31st day, or if the 'preferEndOfMonth' flag is true and
the relevant date is at the end of the month, then the implied convention is 'EOM'.
For example, if the initial date of the sequence is 2014-06-20 and the periodic
frequency is 'P3M' (month-based), then the implied convention is 'Day20'.
If the input frequency is week-based, then the implied convention is based on
the day-of-week of the initial date, where the initial date is the start date
if rolling forwards or the end date otherwise.
For example, if the initial date of the sequence is 2014-06-20 and the periodic
frequency is 'P2W' (week-based), then the implied convention is 'DayFri',
because 2014-06-20 is a Friday.
In all other cases, the implied convention is 'None'.