Adapt to new Poloniex API.

[ghost]

Fixes #20

As the official Poloniex library is broken, here is a custom Poloniex feed, inspired by prior work done by @rodvar in #15.

It provides the same functionality as the old Poloniex feed, while adapting to the new API.

(Plus, there were many unused dependencies in libs.versions.toml, I cleaned it up).

Sample run:

Aug-22 17:43:17.769 [Timer-21] INFO  b.p.s.p.Poloniex: refresh took 490 ms. 
Aug-22 17:43:17.769 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/ETC: 5.94E-4 
Aug-22 17:43:17.769 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/DOGE: 2.427E-6 
Aug-22 17:43:17.769 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/ZEC: 9.76E-4 
Aug-22 17:43:17.769 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/DCR: 4.92E-4 
Aug-22 17:43:17.770 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/LTC: 0.002483 
Aug-22 17:43:17.770 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/XMR: 0.005596 
Aug-22 17:43:17.770 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/ETH: 0.06275 
Aug-22 17:43:17.770 [Timer-21] INFO  b.p.s.p.Poloniex: BTC/DASH: 0.001013 

[rodvar]

I've also tested it. All tests pass now (its broken in main since Polinex test is not passing as the PR properly explains).

Also I can see it getting poloniex rates back again now! :)

   Aug.-23 16:06:41.935 [Timer-20] INFO  b.p.s.p.Poloniex: refresh took 480 ms. 

Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/XMR: 0.005568
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/ETH: 0.0629
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/ZEC: 9.68E-4
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/DASH: 0.001013
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/DCR: 4.92E-4
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/DOGE: 2.396E-6
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/LTC: 0.002492
Aug.-23 16:06:41.935 [Timer-20] INFO b.p.s.p.Poloniex: BTC/ETC: 6.0E-4

[ghost]

@alvasw I have updated this PR to migrate to WebClient, based on #26

[alvasw]

Good work!!

Nit

1. Do you know why we removed Coinbase in the past [1]?

2. WebClient supports JSON Arrays and can return these as Flux objects (see code review suggestions).

I pushed the suggestions too: alvasw@c958d25

[1] 453931b

[ghost]

@alvasw, thanks for the detailed review! Changes applied.

1. Do you know why we removed Coinbase in the past [1]?

Perhaps Coinmarketcap was removed because the API switched to requiring a key. As far as I'm aware we don't use any APIs that require keys. [Disclaimer: don't know the actual history].

[alvasw]

utACK

[gabernard]

utACK