Implement the rest v2 candle and wallet services

[wyaeld]

Inspired on the work started in bitfinexcom/bitfinex-api-go/pull/84, but adjusted to try and fit with the more recent patterns, and fleshed out

• history and last sections split into separate operations
• added a params struct to manage the optional params on the service
• included the example program to demonstrate usage

Rebased when opened. I don't know how to write an actual integration test, but the example program works

@prdn @brobits Please review

[brobits]

Thank you for your contributions to the Bitfinex Go API. Also thanks for including an example program to demonstrate usage, it does help when reviewing. Don't worry about the integration test right now, we don't seem to have a complete pattern for REST yet (this is the closest I think https://github.com/bitfinexcom/bitfinex-api-go/blob/master/v2/rest/book_test.go). I do have a few suggestions of minor things I'd like to see, and I'd be happy to help write a quick integration test once the interface looks good to get this into the repository.

I do appreciate your diligence and adhering to the API pattern. I'm sure other users would like to see these changes added.

[wyaeld]

@brobits Just got back from holiday and taking this up. Made changes to the candle service, implementing some custom types to replace the struct, and splitting the history method into 2 versions, both with example usage.

[wyaeld]

also added a very simple wallet service with example

[wyaeld]

@brobits @prdn can someone take a look at this, the feedback has been included

[wyaeld]

@brobits @prdn Bit concerning if neither myself nor other contributors can get a response. I see new PRs open for over a week with no comment. I expect people have lots of various priorities, but plenty of us are trying in good faith to improve this client, and would really like a little support.

[brobits]

@wyaeld 👏