update docs with new filter functionality

README.md

@@ -237,6 +237,65 @@ Errors:
 * 400 - missing mandatory argument (driven from the arguments on the actual functions)
 * 400 - argument failed validation
 * 500 - server error
+	   
+Filters
+-----------------
+
+There is support for CorePost resource filters via the two following *corepost.filter* interfaces:
+
+	class IRequestFilter(Interface):
+	    """Request filter interface"""    
+	    def filterRequest(self,request):
+	        """Allows to intercept and change an incoming request"""
+	        pass
+	
+	class IResponseFilter(Interface):
+	    """Response filter interface"""
+	    def filterResponse(self,request,response):
+	        """Allows to intercept and change an outgoing response"""
+	        pass
+
+A filter class can implement either of them or both (for a wrap around filter), e.g.:
+
+	class AddCustomHeaderFilter():
+	    """Implements a request filter that adds a custom header to the incoming request"""
+	    zope.interface.implements(IRequestFilter)
+	    
+	    def filterRequest(self,request):
+	        request.received_headers["Custom-Header"] = "Custom Header Value"
+	
+	class Change404to503Filter():
+	    """Implements just a response filter that changes 404 to 503 statuses"""
+	    zope.interface.implements(IResponseFilter)
+	    
+	    def filterResponse(self,request,response):
+	        if response.code == 404:
+	            response.code = 503
+
+	class WrapAroundFilter():
+	    """Implements both types of filters in one class"""
+	    zope.interface.implements(IRequestFilter,IResponseFilter)
+	
+	    def filterRequest(self,request):
+	        request.received_headers["X-Wrap-Input"] = "Input"
+	    
+	    def filterResponse(self,request,response):
+	        response.headers["X-Wrap-Output"] = "Output"
+
+
+In order to activate the filters on a CorePost resource instance, you need to pass a list of them in the constructor as the *filters* parameter, e.g.:
+ 	   
+ 	   
+	class FilterApp(CorePost):
+	    
+	    @route("/",Http.GET)
+	    def root(self,request,**kwargs):
+	        return request.received_headers
+	
+	def run_filter_app():
+	    app = FilterApp(filters=(Change404to503Filter(),AddCustomHeaderFilter(),WrapAroundFilter(),))
+	    app.run(8083)
+
 	    	        
 Performance
 -----------