Added multiple exchange support and trailing zeros option

Great work on the menu ticker!

I really liked it, so I decided to work on it a bit and add support for multiple exchanges. While I was at it, I added BTC Central, Bitstamp, Bitcoin-24 and BTC-e. I've also added an option to toggle whether or not trailing zeros should be stripped, refining the current implementation that dealt with decimals into two cleanly seperate cases.