Properly resolve relative paths in CSS imports

[MatthewCash]

Currently, WebCord cannot resolve relative imports because it simply constructs a new URL() with the relative URL which will fail.

This change passes context about the current file to parseImports and fetchOrRead to prepend the previous URL's directory name if creating a URL fails.

[SpacingBat3]

Thanks to contributing to WebCord!

I overall think the code introduces a lot of redundancy, I won't pull this until either you or I will resolve them. Also, it touches some irrelevant pieces of the code [comparing] to the overall topic of this PR, I guess explaining your approach a bit more and why you haven't considered the others would help me understand your intentions.

[SpacingBat3]

You don't have to force-push PR on changes to have a specific history, in fact it might be better to commit on top of the another. As long as things are around single thing to be implemented, I can always squash your commits later, and having the history of changes done to this PR is for sure useful if we consider to go back to how things were before (isn't that main purpose of git?)

[SpacingBat3]

You still need to resolve some things before I will be willing to pull it (I've made new comments around that).

[SpacingBat3]

LGTM 🎉.