Control over buffering of comments #272
Description
Currently comments are buffered entirely for the comment handler.
Documents with pathologically long comments can hit the memory limit, and the user has no way of preventing that, other than not using comment handlers.
It's wasteful and unnecessary if the handler intends to remove comments.
I think we could add some control for it, e.g. add a configurable maximum length of comment to buffer. If the comment is longer than this, then discard the entire comment (with 0 buffer len acting as automatic comment removal). Another option could be to split the comment and handle it in fragments, but that would be as complicated as text chunks (#256).