Implement Zeller's Congruence
Month#to_s now starts on correct day of week.
Refactor year to Year class
Month#length and Year#leap_year?
Complete printing months, with correct spacing
Month error cases
Error cases for printing years
Year#header implementation
Implement printing years.
Refactor Month#to_s to match the pattern of Year#to_s
Some final tweaks for readability.
Yet another possible implementation of to_s
Another variation on the to_s theme
A yet shorter Month#to_s