If there is ever a question, "but what should this function do under $guarantee?", exclude it or restrict it.

append:
    We guarantee that rows are never deleted
        - No free-list
        - No retain
    But all tables are clearable!

public:
    We guarantee that foreign tables learn about existential changes
        - Row deletions require use of free-list
        - Insertions & deletions must be logged
        - Write lock requires flush() or skip_flush()

foreign key:
    You must implement an event handler; there's helper functions.
    You can call 'join'

sorted:
    We guarantee that the rows are kept sorted:
        - can only insert via sorted iterable.
        - #[sort] field is immutable.
        - Sorted tables can't have trackers. (insert at front == spam)
        - No #[index] allowed. (The primary key does act as one)
        - Unchecked rowids can't be made.
    User must implement (or derive?) Ord for Row. Keep in mind that #[derive(Ord)] may give you more sorting than you'd want.

free list:
    Rows can be marked as 'deleted'
    Deleted rows are not iterated over
    New rows overwrite deleted ones

join:
    What if we want to do a merge-join? Well. It's NEVER a merge join!

column indexes:
    We guarantee that indexed columns are always up to date.
        - #[index] field can not be modified








# Unimplemented:
bag:
    We guarantee nobody's watching:
        - Unchecked rowids can't be made
        - Order is arbitrary. (Delete == replace w/ pop())

array:
    Like 'bag', but order is preserved