Remove the 'ERROR is unimplemented' documentation

.. because it's confusing, since errors are implemented but all errors
are considered fatal, as documented.

Author: jay

README.md

@@ -52,14 +52,10 @@ line then the warning applies to the old version of the file, and if the line
 above a warning is an added line then the warning applies to the new version of
 the file.
 
-On error a line that starts with `ERROR:` and is followed by script name and
-error message(s) --which may be one or more lines-- is sent to standard error
-output (stderr). The script then continues to the next line.
-***This is unimplemented for now. All errors are treated as fatal errors.***
-
-On fatal error a line that starts with `FATAL:` and is followed by script name
-and error message(s) --which may be one or more lines-- is sent to standard
-error output (stderr). The script then aborts with exit code 1.
+All errors are sent to standard error output (stderr). Currently all errors are
+treated as fatal errors. On fatal error a line that starts with `FATAL:` is
+followed by script name and error message(s), which may be one or more lines.
+This script then aborts with exit code 1.
 
 Examples
 --------

showlinenum.awk

@@ -67,14 +67,10 @@
 # above a warning is an added line then the warning applies to the new version
 # of the file.
 #
-# On error a line that starts with ERROR: and is followed by script name and
-# error message(s) --which may be one or more lines-- is sent to standard error
-# output (stderr). The script then continues to the next line. This is
-# unimplemented for now. All errors are treated as fatal errors.
-#
-# On fatal error a line that starts with FATAL: and is followed by script name
-# and error message(s) --which may be one or more lines-- is sent to standard
-# error output (stderr). The script then aborts with exit code 1.
+# All errors are sent to standard error output (stderr). Currently all errors
+# are treated as fatal errors. On fatal error a line that starts with 'FATAL:'
+# is followed by script name and error message(s), which may be one or more
+# lines. This script then aborts with exit code 1.
 #
 ####
 #