EPIC: new iavl library is not implemented

[yihuang]

Implement the ideas described here.

• Problem: memiavl package is not standalone #877
• Problem: memiavl snapshot format is not optimal #890
• Problem: export API not supported in memiavl #924
• Problem: memiavl import API not implemented #941
• Problem: memiavl interator not implemented #951
• Problem: memiavl don't support async snapshotting #948
• Problem: memiavl changes are not persisted in real time #947
• Problem: memiavl don't support store upgrades #960
• Problem: memiavl operations on multiple stores are not atomic #961
• Problem: memiavl don't support ics23 merkle proof generation #976
• Problem: old snapshots are not pruned #964
• Problem: memiavl rootmulti integration is not thread-safe to use #977
• Problem: memiavl revisit the integer overflows handling #980
• Problem: memiavl is not integrated into rootmulti store APIs #938
• Problem: memiavl snapshot rewriting is not triggered #981
• Problem: memiavl cache store is not optimal #982
• Problem: memiavl secondary snapshot format not implemented #923
• Problem: memiavl has relatively big gc pressure #988
• Problem: memiavl don't read multiple historical snapshots #1007
• Problem: memiavl, zero copy or not? #1009
• Problem: memiavl persisted node queries is not optimal #1016
• Problem: memiavl documentation is not complete #1017
• Problem: memiavl db is not protected against multi-processing opening #1055
• Problem: memiavl more efficient snapshot setup is not used #1067
• Problem: memiavl don't support rollback #1089