checks for easter date calculation
refactor
validation of parameters for FixedHoliday and NextMondayHoliday
whitespace change

writing things this way makes vim syntax highlighting happy. To be
checked and fixed, some day
removed TODO; ruby doesn't have nice slicing methods
validate arguments for easteroffset holidays
argument checking for holidays_in_period
corrected typo in holiday name
moved country list to the Holiday module
removed now-unused todo