--content-charset option required

Hello,

When setting --content-type and --content-name in my opinion --charset
option is missing for subsequent attachments or for the standard
input.

I can set it with:
" -a \"Content-Type: text/html; charset=utf-8\" " for stdin, but it is
not working for text/html

I think it shall be there, in the same sense as the other content
options.

Jean