last + open → this.sum (last, open) in parseTicker for bithumb, bitme…

…x, cryptopia, hitbtc2, huobipro, poloniex fix ccxt#2066

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_1btcxe ticker timestamp and parseDate added to js/py/php

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added a comment on Console/Table.php to examples/php/arbitrage-pairs.php

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added missing metainfo fields to zb.has ccxt#1300 ccxt#1717

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one more minor rule to CONTRIBUTING.md

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added a workaround for shared cache problem to python

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added support for origClientOrderId to binance fix ccxt#2064

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added a float.toString warning to CONTRIBUTING.md ccxt#1300 ccxt#1717

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added examples/js/okex-fetch-ohlcv-since-limit.js ccxt#2062

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skip xbtce on Travis

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