Add update insert (upsert/upinsert...) functionality

[Viatorus]

I'm submitting a...

[x] Feature request

Current behavior

Currently, there is no function to do a simple update insert of a document.

Expected behavior

Provide a method to insert or update a document to the collection. The function should check by using unique indices if the document should be inserted or update an existing one.

See techfort/LokiJS/issues/158

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

Long requested feature. Many databases support this.

[xkem]

^^^^^^^^