Support for go-ipfs v0.5

[lidel]

This is a notice I'm filling in repo of every HTTP Client I can find.
Feel free to close it if this project already works fine with go-ipfs 0.5

POST-only HTTP API

go-ipfs 0.5 will block GET commands on the API port (ipfs/kubo#7097), requiring every command (RPC) to be sent as HTTP POST request.
See API reference docs: https://docs.ipfs.io/reference/api/http/

This is potentially a breaking change,
double check if this project uses POST for every RPC call.

Testing

Download links for v0.5-rc* are available at ipfs/kubo#7109

You can also test using an ephemeral Docker container:

$ docker run --rm -it --net=host ipfs/go-ipfs:v0.5.0-rc1 

[gkbrk]

This is now done. We haven't reached future-parity with the old version yet, but most of the core functionality seems to be working. I pushed an intermediate version to crates.io for now. I expect that the rest of the methods will be finished soon.