lib: cache the get_price() data

We'll call get_price() frequently when we need buy price and sell price
We cache the data for 5 seconds now, so that we can avoid at least one
API call when we need buy and sell price data.

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>
lib: get new price if we call get_price() in 5 seconds

Will try getting new price if we call get_price() in 5 seconds, but with
different label.

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>
bot: add set_label()

add set_label() so that we can change the target currency anytime.

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>
bot: add btc/ltc/doge auto trading bot

This is new design bot that it won't make the order until it hit our
target price. It will monitor 3 coins at the same time and try to
make the order when the price hits our target price.
So, it won't waste the money by placing them on the orders, only places
orders when needed.
BTW, it doesn't check if the order we placed success or not, so we might
get some open orders. We have to cancel them manually.

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>
3bot: cancel orders if the deal is not done

We'll cancel the orders if the deal is not done in 10 ticks(around 1 minute)

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>