 ICU standards for numbers formatting works partially

As described in the readme:

> Message format is strictly implemented by ICU standards.

But I tested the number formatting from here:

> https://unicode-org.github.io/icu/userguide/format_parse/numbers/skeletons.html

and most of the examples don't work, such as:

```
{value, number, ::.####}
```

or

```
.00/w
```

But

```
{value, number, ::.0####}
```

works