Review "conditional close" example parameters

[veox]

Reported in #94 (search "sanity check") - the conditional close example might have become incompatible with the current Kraken API.

[veox]

The example is good - just tested again for issue #124.

The order's close[type] is determined automatically - it'll be complementary to type. So if type is buy, then close[type] is sell, and vice versa.

ordertype must be provided, although the list on Kraken's docs page is outdated. Currently available: limit, stop-loss, take-profit, stop-loss-limit, take-profit-limit, settle-position.

price and price2 depend on ordertype, as their docs say. Other keys in close[] still seem to be ignored.