The safe and stable builder for [`fmt::Formatter`]
Due to unstable [`Formatter::new`], uses this crate to dynamically build a [`Formatter`].
```rust
use formatter_builder::{FormatterBuilder, Fill, Sign, Alignment};
let mut output = String::new();
let n = 6.23;
formatter_builder::FormatterBuilder::new()
assert_eq!(output, "0006.230")
```