Basic CRUD(create, read, update, and delete/cancel) operations

[fnorman]

Implement CRUD operations for the following order types
- Limit Buy
- Limit Sell
- Market Buy
- Market Sell

This means within the OrderBook data structure, there should be a new entry of a Limit Buy, for example, that represents what the user has input. An example function call would be

limitBuy('TSLA', ...)

And the function hides all intricacies from the user. For more information about the various order types, check out this video.

[jaineeshah9]

Assigning to myself (Jainee)