Fix relative URL joining #570

[Sparshsing]

Summary

Fixes #570
Relative url joining has been fixed. The issue was due to incorrect usage of link protection using <> tags.

List of files changed and why

crawl4ai/html2text.py -
While parsing the "a" tags in handle_tag method, the url in "href" attr was being protected by surrounding with <> in the opening tag, and then in the closing tag it was joined with base_url. To fix this, the protetion with <> is done after the url is joined with the base_url.
The same process has been done in the o() method.

crawl4ai\markdown_generation_strategy.py -
In the conversion of links to citations for markdown_v2, we remove the <> symbols from the url if it was protected, then we join the url with base_url.
Also the fast_urljoin method was modified, since it would join a url incorrectly if the base url included a path eg. https://docs.crawl4ai.com/core/crawler-result/.

How Has This Been Tested?

It was tested by generating markdown and markdown_v2 of few urls.
eg. https://docs.crawl4ai.com/, https://docs.crawl4ai.com/core/crawler-result/
The links in the fixed markups were working as expected.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added/updated unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[Sparshsing]

Maybe there should be a check at the top level code to add / at the end of url if not exist, as it can cause issues with relative urls.