Support custom timeout management

[alexgolec]

Is your feature request related to a problem? Please describe.
HTTPX defaults to 5s timeouts, and some users require longer and/or no timeouts.

Describe the solution you'd like
Start using a client object and expose it to the user so they can set their HTTPX settings.

Describe alternatives you've considered
N/A

Additional context
N/A

[codyfletcher]

Hey @alexgolec, great work on tda-api. Thank you! ⭐️

Quick question, are you open to splitting this into 2 separate issues:

1. Explicitly set a longer default timeout for tda-api, say 15-30s? The thought being that—while 5s is a sane default for HTTPX and most projects—TDA can't seem to serve up historical transactions and/or orders within 5 seconds even if the queried date range is narrow (e.g. 2020-06-01 to 2020-06-02).

2. Keep this current issue as-is as a follow up issue. It's a better solution but a more time-intensive one.

[codyfletcher]

Found this on discord. Posting here in case it's of value to others.

import httpx

fine_grained_timeout = httpx.Timeout(5.0, connect=1.0)
tda_client.session.timeout = fine_grained_timeout

[alexgolec]

That's good feedback. I've put together a PR that will address both points.

[codyfletcher]

Thanks @alexgolec, you're CRUSHING it!