send msg for order creation

Feat: able to specify preferred usdt address in request

feat: able to force usdt rate via request so it can support usd payment by set the rate to 1

Fix: incorrect usdt to cny rate

Merge remote-tracking branch 'upstream/master'

Update README.md

Ignore the transactions finished a long time ago

Fix: unable to finish transaction due to inaccuracy of float

Fix: the first wallet was chosen all the time as now the money is random

Trial fix the transaction not honored issue when there is timeskew on the server

Trial fix the timeout query tronscan api

Fix: max order id length validation

Feat: make the order column longer for longer order id

Fix: the check status call might be cached by cloudfront or whatever other cdn

Fix: paid to another use when the sender is very slow to send money