[semidet,multifile]http:status_page(+Status, 
+Context, -HTMLTokens)Hook called by http_status_reply/4 
and http_status_reply/5 
that allows for emitting custom error pages for the following HTTP page 
types:
- 201 - 
created(Location) 
- 301 - 
moved(To) 
- 302 - 
moved_temporary(To) 
- 303 - 
see_other(To) 
- 400 - 
bad_request(ErrorTerm) 
- 401 - 
authorise(AuthMethod) 
- 403 - 
forbidden(URL) 
- 404 - 
not_found(URL) 
- 405 - 
method_not_allowed(Method,URL) 
- 406 - 
not_acceptable(Why) 
- 500 - 
server_error(ErrorTerm) 
- 503 - 
unavailable(Why) 
The hook is tried twice, first using the status term, e.g.,
not_found(URL) and than with the code, e.g. 404. 
The second call is deprecated and only exists for compatibility.
| Context  | is the 4th argument of http_status_reply/5, 
which is invoked after raising an exception of the format
http_reply(Status, HeaderExtra, Context). The default 
context is [] (the empty list).  | 
| HTMLTokens  | is a list of tokens as produced 
by html//1. It is passed to print_html/2.  |