Remove hyperx dep; Manually inspect 'Link' header

[lpotthast]

As stated multiple times in #110, the existence of the hyperx dependency causes more trouble than it brings functionality.

This PR removes the dependency altogether, replacing the small bits which were actually used with some custom logic.

Note:
Alternatively to merging this, one could hope that merging dekellum/hyperx#40 will resolve all our problems...

[oovm]

Please follow up this PR, this branch works fine.

I have encountered some dependency conflicts of percent-encoding and cannot use octocrab in combination with other frameworks.

[drshade]

Thanks - I have tested this and it does seem to fix my dependency conflict relating to hyperx.

My workaround is setting my octocrab dependency to:

octocrab = { git = "https://github.com/lpotthast/octocrab", branch = "remove-hyperx" }

Which allows me to move compile and move forward for now...

[XAMPPRocky]

Thank you for your PR, and congrats on your first contribution! 🎉