Improve PICT compatibility, add batch mode to gpr2gpa

Documentation/userhouses.txt

@@ -55,4 +55,30 @@ Some old QuickTime movies contain movie tracking information in the movie
 resource fork, in which case you need to merge them into the data for modern
 utilities to read them.  You can use the "flattenmov" tool to do this: Pass
 it the data (.gpd) and resource (.gpr) data files for a movie, and it will
-merge them into a single .mov file.
+merge them into a single .mov file.
+
+
+BATCH CONVERSION
+------------------------------------------------------------------------------
+To batch-convert house resource files, use gpr2gpa with a path that ends
+with an asterisk (*) and omit the output filename.
+
+
+SECURITY CONSIDERATIONS
+------------------------------------------------------------------------------
+Glider PRO didn't really do any validation of houses.  Currently, Aerofoil
+doesn't do any additional validation either, and it's possible that invalid
+house data may lead to crashes or even remote code execution.
+
+I will be doing a hardening pass on the loader for the 1.1 release.  Until
+then, please only load houses from trusted sources.
+
+Also, Glider PRO houses were able to take advantage of a resource overlaying
+feature of the Macintosh operating system, where a resource being present in
+the house file with the same ID as an application resource would cause the
+resource to override the application resource.
+
+Aerofoil's resource loader is much more restrictive: Currently, only
+backgrounds, audio triggers, and icons may load from the house data.  This
+restriction will be loosened in the 1.1 release to allow resources to be
+overrided if I can confirm that it's safe to override them.