Improve generic type parameters

[alpha-tango-kilo]

Use AsRef<str> instead of Into<String> where sensible to do so Saves allocations and/or taking ownership Potentially a breaking change on some really weird types

[alpha-tango-kilo]

Rebased on latest master and resolved conflicts. Massively reduced the scope of the changes as there was no harm in using Into<String>/Into<URL> in a lot of places since an owned value was going to be needed anyway (like with all the Request::new aliases)

[alpha-tango-kilo]

CI failure looks to be #93

[neonmoe]

It's been fixed now, rebasing onto the newest master should make the CI pass. The PR looks great!

[alpha-tango-kilo]

Thanks for the fix, all rebased!