First attempt at IERS A, B table classes, interpolation of UT1-UTC.
Cleanup of logical vs integer, use of super.

Correct bug introduced with previous commit
Memoize IERS_A and IERS_B: tables can be kept for session.
Initial linkage to time, with only simple exception messages.

Correction to linkage to Time
First test cases -- if for nothing else than stop me from some silly mistakes
Cleanup of interfaces

Cleanup of interfaces
Moved IERS-B data and both readme's to data subdirectory
Adapt setup_package.py to include iers/data files
Add documentation, some tests, ensure ReadMe's work on .gz files
Simplified Time part; added IERS A tests; document how to use A if needed
Remove documented trickery that's unlikely to remain (or be needed).
Next iteration: exception in ut1_utc, safer memoization