Converts `self` to little endian from the target's endianness.
On little endian this is a no-op. On big endian the bytes are swapped.
# Examples
Basic usage:
```
# use ::exint::primitive::*;
# ::exint::uint! {
let n = 0x1A_u24;
if cfg!(target_endian = "little") {
assert_eq!(n.to_le(), n)
} else {
assert_eq!(n.to_le(), n.swap_bytes())
}
# }
```