StreamComment allows comments to be put onto the stream. TODO: consider that comments should be sourced by the stream producer, but what about comments from filters? That is, if I'm a filter and I produce comments, should I throw out the comments I receive?
task progress comments are either of the form:
 {@code
   [xx]000000   or
   [xx]000000 for indeterminate
 }
   
 These are currently unimplemented!
log comments are of the form:
 {@code
   [xx]000000   or
   [xx]000000
 }
   
 
 Note the log level should be requested by the client.