Changes for DateTime::Set

0.20
- Docs for DateTime::SpanSet API 
  (not implemented)

0.19
- DateTime::Span API: 
  from_datetime_and_duration, from_datetimes

0.18
- changes docs, changed API
  from_recurrence, from_datetimes, new()
- as_list

0.17
- previous() method (quite untested)

0.16
- small API changes

0.15
- revised docs, from Dave Rolsky
- small bugfix in creating open spans

0.14
- added DateTime::Span and DateTime::SpanSet
- put "..." to mark where we need more docs
- DateTime::Set and DateTime::Span API look ok.

0.13
- added tests for set operations with recurrences/add

0.12
- iterator passes all tests
- the API is complete, as described in SYNOPSIS
- small fix in add() syntax; accepts a duration=> parameter

0.11
- iterator, next

0.10
- union, intersection

0.09
- experimental code to generate recurrence from a simple callback

0.07
- added experimental method create_recurrence()

0.06
- added experimental method add_duration()

0.05
- improved SYNOPSIS
- added 'immutability' tests
- new() will not try to clone non-DateTime parameters (such as the
  Infinity value)

0.04

- The program will die with an error message, 
  if one tries to use offset() or quantize() methods
  These methods might come back in a later version.

- new() clones its parameters.
  This means the parameters don't have to be immutable

- new() will give an error message if we try to use a scalar parameter
  instead of a DateTime

0.03

- Uses Set::Infinite as base class, instead of Date::Set::Timezone
  This means some methods just disappeared, like event() and exclude().
  RFC2445 support might come back in a later revision.

- Removed experimental Autoload code

- Added 'Changes' and 'README'

- moved POD to end of source file.

