Separate out parsers and tests
Rename isodatetime remnant
Add type checking, fix bugs
Restructure & rename files
Improve dumping capability
Dumper fixes
fix dumper
Centralise constants and error messages.

This implements feedback from @matthewrmshin.
isodatetime: fixes
isodatetime: fix time zone dumping
isodatetime: implement feedback
update memoize-decorator caching
improved documentation
centralise caching limit
Merge pull request #17 from benfitzpatrick/split-up-file

Separate out code into different modules; better dumping capability.
metomi/isodatetime#13: timepoint-like duration e.g. PYYYYMMDD
test timepoint membership in timerecurrence
Add CHANGES.md file
Merge pull request #23 from benfitzpatrick/test_in_timerecurrence

Test for membership in TimeRecurrence
isodatetime: fix recurring recurrence format 1