Use better endpoint for bittrex pct-chg scripts

[nmielnik]

Right now the pct-chg-bittrex and trade-bittrex scripts are both querying for the last 200 trades for each coin individually, and building up a cache over time to monitor big swings. However, since it's on the last 200 trades, for coins with a lot of volume the script can't built up much of a history until it's been running for a while.

There is a public url that's not documented which could make this a lot easier to do, since it's the same url used to get the candlestick data for generating the graphs (this is the exact kind of data needed by the script)

https://bittrex.com/Api/v2.0/pub/market/GetTicks?marketName=BTC-ARK&tickInterval=oneMin

That url should work for any coin, changing BTC-ARK to be any specific pair...from there, might even be able to get the last ticker value for all coins in a single query and just ping that every 30 seconds or so...we'll see.