pub fn to_digit(c: char, radix: uint) -> Option<uint>
Convert a char to the corresponding digit.
If c is between '0' and '9', the corresponding value
between 0 and 9. If c is 'a' or 'A', 10. If c is
'b' or 'B', 11, etc. Returns none if the char does not
refer to a digit in the given radix.
Fails if given a radix outside the range [0..36].
Prefix searches with a type followed by a colon (e.g.
fn:) to restrict the search to a given type.
Accepted types are: fn, mod,
struct (or str), enum,
trait, typedef (or
tdef).