Refs #93 -- Revert URL regex and validate URLs separately

[amureki]

My initial regex in #93 is not handling correctly URLs without a scheme/www, so I have no better idea here but:

• parse for everything that seems like a markdown link
• validate URL and scheme and apply things only to places we want

[codingjoe]

I am not so sure if I understand what went wrong. Maybe you could elaborate more?

[amureki]

I am not so sure if I understand what went wrong. Maybe you could elaborate more?

As I wrote in PR description, UTM injection into certain links was failing with the new regex. And my new tests are covering the failing cases:

[A link without a scheme](www.example.com)
[A link without www](example.com)
[ALL CAPS LINK](HTTP://WWW.EXAMPLE.COM)
[localhost:8000](http://localhost:8000)

[codingjoe]

There is still some duplication, but it looks good to me 👌