#26 Configurable parser WARNINGs

[Vlad Skarzhevskyy]

Example:
WARNING: lacks "summary" attribute
http://www.w3.org/TR/1999/REC-html401-
19991224/struct/tables.html
As I see summary #IMPLIED so is optional.

Also there may my be some other wanings that would
be important for one application and not important for
another. Like alt for image wich is #REQUIRED but
some time not realy important for me during
development.