iso_8859_default decoding is changed to us_ascii. Purpose - header cleanup,
if mailer adds non-encoded 8bit symbols in header. Other iso-8859-x charsets
are supported. Original function is shorter, but it is hard to count all ?.
ns_4551_1 decoding might need some adjustments.
Added basic @package/@subpackage tags
The decode/ files were documented slightly more thoroughly, although they're almost self-explanatory anyway.
The individual functions in the functions/ files need to be documented though, and now that this commit is in, anyone willing to write docblocks for functions should get cracking ;)
