Adapt requests to use new request handler framework from swarm

[gavin-norman-sociomantic]

Swarm v4.5.0 includes a PR to convert the global status codes into a supported/not supported code.

All requests in dhtproto neo should be updated to use this system, rather than the old approach of an unsupported / ok / error status code. (The idea is that the initial status code purely indicates whether the node supports the request or not, and all actual errors are handled by messages that can be passed at any time, not just at request initialisation.)

• GetHashRange
• Put
• Get
• GetAll
• GetChannels
• Mirror (Use new request handlers framework from swarm #94)
• Exists
• Remove
• RemoveChannel

[gavin-norman-sociomantic]

One commit in the PR gives an example of adapting a request: sociomantic-tsunami/swarm@96a2c38

[gavin-norman-sociomantic]

This is a protocol change. Existing requests could be adapted via a new request version, but as we're in alpha still, backwards compatibility is of low importance. I'll simply do this as a breaking change.

[gavin-norman-sociomantic]

#90 adapts Get, Put, GetChannels, Mirror.

I'll do GetHashRange and GetAll as part of #70 and #38.

[gavin-norman-sociomantic]

All done except GetAll. Waiting until sociomantic-tsunami/swarm#243 is implemented.

[gavin-norman-sociomantic]

GetAll was actually done in aacd1fa, as part of the major submodule update.