Makes a copy of the value in its ASCII upper case equivalent.
ASCII letters 'a' to 'z' are mapped to 'A' to 'Z', but non-ASCII letters are unchanged.
To uppercase the value in-place, use [`make_ascii_uppercase`].
[`make_ascii_uppercase`]: Self::make_ascii_uppercase
# Examples
Basic usage:
```
# use ::exint::primitive::*;
# ::exint::uint! {
let lowercase_a = 97_u8;
let uppercase_a = 65_u8;
assert_eq!(uppercase_a, lowercase_a.to_ascii_uppercase());
# }
```