Parses an integer from an ASCII-byte slice with digits in a given base.
The characters are expected to be an optional `+` sign followed by only digits.
Leading and trailing non-digit characters (including whitespace) represent an
error. Underscores (which are accepted in Rust literals) also represent an error.
Digits are a subset of these characters, depending on `radix`:
* `0-9`
* `a-z`
* `A-Z`
# Panics
This function panics if `radix` is not in the range from 2 to 36.
# Examples
Basic usage:
```
# use ::exint::primitive::*;
# ::exint::uint! {
assert_eq!(u24::from_ascii_radix(b"A", 16), Ok(10_u24));
# }
```
Trailing space returns error:
```
# use ::exint::primitive::*;
# ::exint::uint! {
assert!(u24::from_ascii_radix(b"1 ", 10).is_err());
# }
```