Brainstorm a generic appender interface

[MrPowers]

We have two different types of appends now in mack:

• append_without_duplicates
• constraint_append

We might want to think of a more generic interface that will allows for mixing & matching of the different append modes. Users might want to use both.

Perhaps something like this: mack.appender.without_duplicates(delta_table).constrained(delta_table, quarantine_table).

Are we going to want to add other types of append functionality as well?