Some new bag theorems, and some syntax cleanup within the script.

Cleanup includes flipping to tight_equality (temporarily so as not to
contaminate descendents), and putting in a bunch of <=> instead of =
where necessary).
Clean quotient examples: now use core Mutual lib, rather than own copy

This is a start, of sorts, on having a go at github issue #10
BasicProvers ind'n tacs more uniform on datatypes and "non-datatypes"

Includes test-case of sorts.