Add base64.

Add base64.

The tizen guys wanted this. Yeah, I know there's base64 code in
uuencode/uudecode, but that this has -i, input lines aren't of fixed length,
encode/decode are in same file, there's no prefix/suffix code, it always
writes to stdout... Eliminating the code duplication wouldn't be worth
the if/else I'd have to add, so I just did a new one.

Factored out the base64 table init into lib.c though: that was worth sharing.