Make Spider importable from main module

[Mews]

Feels like you should be able to do from tiny_web_crawler import Spider, not just from tiny_web_crawler.crawler import Spider

Would be as simple as adding from tiny_web_crawler.crawler import Spider to __init__.py

Edit:

• Update how we import the package and update the readme usage doc (moved from Housekeeping: Refactor the Spider class to reduce the max args. Use a dataclass #9 )

[indrajithi]

I think we should prioritise this because after #9, our usage doc is outdated. We can also consider releasing a beta version v.0.4.0-beta.1 and make sure the current changes are working.