Allows the user to set the precision for their exchange rate values.
Config setting:
```
exchangerates:
precision: 3
```
Default is `7`.
Also aligns converted values along the decimal place for improved
aesthetics.
Signed-off-by: Chris Cummer <chriscummer@me.com>
This purely happend due to maps not keeping the order items are in. This way
it at least won't change throughout the runtime of wtfutil. Ideally it would
use and keep the order as specified by the user in the configuration but
right now there is no way to enforce this.
