Version bump to 1.0.0
two major additions

  - if you pass a range of Dates to each_day, it will yield a single Date
    instance instead of a range. In the range which used to be yielded, the
    begin and end values were always identical (since we're iterating over dates
    one day at a time, with a step size of 1 day).
  - added iterate_days, which is the same as iterate except that step_size is
    specified in days instead of seconds.
update README for 1.0.0
Regenerate gemspec for version 1.0.0