Changed the return of the function to bool

This will suite other needs much better in the future.
Cleaned up old code

Removed the code that doesn’t work.
Added a calc_month function

Function takes a date and number of month days against which we check
if it is grater than. If it is we subtract the same number and add
another month to the date.
Removed the old check leap in adder function

We do this in order to accommodate the new, cleaner, from of is_leap
function.
Completed the adder function with comments

We add comments and do the function using the new calc_month function
to make the code and execution a little cleaner and easier to
understand.