Encode a single address ready for internet usage.
Header folding as per rfc822 is also performed, based on the length *len. If len is
null, then no folding will occur.
Note: The value at *in will be updated based on any linewrapping done
| len |
the length of the line the address is being appended to |
| name |
the unencoded real name associated with the address |
| addr |
the routing address |
|
the encoded address |