Daniel Karzel 1d62f4916c
Move max_buy and ask_spread into config
Max-buy and spread is not something that one would configure on every run.
More convenient to keep this in the config.

The max-buy Bitcoin value was adapted to `0.02` which is more reasonable for mainnet.
Activated feature `serde-float` to serialize the spread (Decimal) as float instead of string.

```
...

[maker]
max_buy_btc = 0.02
ask_spread = 0.02
```
2021-05-11 12:02:57 +10:00
..