bump reqwest to 0.11, make async,

[C0D3-M4513R]

supercedes: #7 fixes: #5

Draft, because I still want to look the changes over myself before a merge. Edit: Looked this over once again, and this seems reasonable, as long as this ends up being a major version bump.

Be aware, this is a breaking change, but imo less bad than #7, because non-blocking is the way to go.