Add client.EnableFiddlerDebugProxy().

Fixes bchavez#7 - Make MaxMarketFunds / MinMarketRate nullable. Fixes…

… JSON deserialization error with `client.MarketData.GetProductsAsync` when using sandbox.

Fixes bchavez#6. Use nullable decimal on TickerEvent for BestBid and …

…BestAsk.

Prep v2.0.3.

Add GetErrorMessageAsync() extensions for exception error handling.

prep release

docs

update history prep release