%error, %warning out on the final pass, add %fatal

Only process %error or %warning directives on the final pass.  Add a
new %fatal directive which terminates assembly immediately.
diff --git a/doc/changes.src b/doc/changes.src
index b39d3a5..ea0a4c7 100644
--- a/doc/changes.src
+++ b/doc/changes.src
@@ -14,6 +14,10 @@
 
 \b New \c{%warning} directive to issue user-controlled warnings.
 
+\b \c{%error} directives are now deferred to the final assembly phase.
+
+\b New \c{%fatal} directive to immediately terminate assembly.
+
 \b \c{__utf16__} and \c{__utf32__} operators to generate UTF-16 and UTF-32
   strings.