[tz] Proposal for new rules

[Stephen Colebourne]

A simple proposal to move forward from where we are with reliable new rules:

1) Each inhabited ISO-3166 region must have at least one fully defined
zone (LMT, pre and post 1970)

2) Links must not cross ISO-3166 region bouindaries

Some of the rules that would require reworking (not a complete list):
Europe/Busingen
America/Atikotan
America/Aruba
America/Anguilla
America/Port_of_Spain
Europe/Zagreb
Europe/Vatican

Note that America/Montreal does not require reworking as a result of
the first two new rules, although since it looks to have detailed
historical information it would be unwise to lose that. Therefore I
would add a third rule:

3) Existing pre-1970 data shall be respected

If accepted, then these rules would be encoded in the theory file.

Stephen