Changed format string 'X' to 't'
Added lower and upper case base-16 serializations

Use "%x" for the lower-case base-16 serialization and "%X" for
the upper-case.
Add base-10 serialization
Added generic and unsigned base-10 serialization

The unsigned base-10 code is simply a placeholder right now. It
needs to be updated to be different from base-10 serialization
when the negative sign is added to Integer.