new store

[jafri]

Simpler store proposal for new users:

• Removed next available primary key tracking from mi.ts
• Creates store.ts that does operations by value
• Tests for store.ts

Still missing, will add soon:

• Find functions for secondary indexes
• Tests for store.ts secondary index

Any feedback @learnforpractice ?

[learnforpractice]

I've been thinking MultiIndex is good enough for use.

We don't want a duplicated implementation, That will cause confusion.