add transaction history pagination support

[mattypiper]

Problem addressed

Some of the tastyworks endpoints need to be paginated. this PR adds pagination for the transactions (history) endpoint.

I refactored tastyworks/models/trading_account.py to save the session into the account object. It seemed cleaner to me. If you don't like it, I understand rejecting the PR. But feel free to use what I learned about history pagination in your own way.

Solution

Use HTTP GET request arguments "start-at", "end-at", "per-page", "page-offset"
Use HTTP GET response parameters "pagination" and "total-pages"

Checklist

• PR commits have been squashed
• All tests pass
• Code adheres to contributing guidelines

[mattypiper]

I modified example.py a little bit too to print out (test) the transaction history. I'm sure order history (and other endpoints) can support the same style of pagination using the API params, but I haven't played with that yet.

[mattypiper]

closing in favor of #64