:sig
f64 to_f64(String s, f64 fallback = 0)

:params
s : string to parse
fallback : value returned when `s` is empty or not a complete floating-point number
return value : parsed f64, or `fallback`.

:see
>types
to_u64
to_s64
to_bool
float_val

:content
Parses a trimmed string as a floating-point number.

Unlike `float_val()`, the whole trimmed string must be consumed by the parser. Empty strings and partially parsed values such as `"3.5ms"` return the fallback.

```uce
f64 timeout = to_f64(context.server->config["REQUEST_TIMEOUT"], 15.0);
```