Prints the string "WARNING: " followed by any arguments and/or content to the Water console window,
and returns the resulting string output.
Arguments or content are usually strings but can be any objects.
Example: A simple warning
<warning "A warning message." />
"WARNING: A warning message."
Example: Multiple objects in a warning
<warning 4.<plus 1 /> " and "><plus 4 2/></warning>
