No currency exchange rate

[arkanoider]

Hi @grunch @bilthon ,

did some refactoring for error messages on Yadio request, should be better now:

• If 4 retries are over we get:

MostroError::NoAPIResponse => write!(f, "Price API not answered - retry")

• No currency exchange on Yadio list:

MostroError::NoCurrency => write!(f, "Currency requested is not present in the exchange list, please specify a fixed rate"),

• Malformed answer from Yadio

MostroError::MalformedAPIRes => write!(f, "Malformed answer from exchange quoting request")

[arkanoider]

Added a check to use fixed amount rate specified by user when new order is created.

Example:
mostro-cli neworder -k sell -a 20000 -c XMR -f 10 -m SEPA

Now takes 20000 sats as the amout the user want to exchange for 20 XMR, before we asked to Yadio api anyway causing wrong quote or no quote imo.

Let me know

[arkanoider]

Added an extra check in order.rs to avoid negative amount ( with fixed or calculated ), don't know if it's necessary, but could be an extra safety check.

Feel free to merge it or no...easy to remove!

[grunch]

LGTM