class Date

def advance(options)

any of these keys: :years, :months, :weeks, :days.
Provides precise Date calculations for years, months, and days. The +options+ parameter takes a hash with 
def advance(options)
  options = options.dup
  d = self
  d = d >> options.delete(:years) * 12 if options[:years]
  d = d >> options.delete(:months)     if options[:months]
  d = d +  options.delete(:weeks) * 7  if options[:weeks]
  d = d +  options.delete(:days)       if options[:days]
  d
end