Removed peek and pop
Changed auto-flatten to use append-flat rather than conj to add elements
Made append-flat into protocol and named it conj-flat
Changed name of type to AutoFlattenSeq
Revert "Changed name of type to AutoFlattenSeq"

This reverts commit 94ceb2c5df396a1dffe96d654ff8b85b2129944a.
Changed name to AutoFlattenSeq
Cache the sequence in auto-flatten-seq