Replace rbtree with b+tree

[M1Les]

This contains two changes.

1. Adding an alternative tree library (ordered-btree) to use for indexing inside of in-memory provider. We noticed that red-black-tree has a bug in it that causes it to go into an infinite loop when the tree is being rebalanced. This change makes it possible to choose between the two libraries when database is created.
2. A small fix for non-unique indices. When an item is removed from the store, non-unique index it is part of, will be reset to undefined:
   

ind.remove will remove all values from the index, even if there are multiple items in that index (in case of non-unique index).

In this fix we're splitting remove operation in two steps for non-unique indices:

• Find the index value (array of items with the same index)
• Using primary key, locate and remove the item from the array

There are possibly some performance implications to doing array.filter to remove the item, but could not come up with a better way of removing item without iterating over all array items -- yes, we can stop comparing pks after the first match, but we still need to go over the rest of items to finish copying the array.

[thomastay]

left some feedback

[thomastay]

Also, looks like the CI build is failing because of lint issues with prettier

[M1Les]

Yeah, it was failing before because of the other PR, it was not able to reuse the same version tag. Still fixing it

[Sudhar123]

add a comment above the remove for non-unique/unique indices

[thomastay]

Comments look good