convert flat hash to nested data using TT2's dot convention

 Converts a CGI query into structured data using a dotted name
 convention similar to TT2. expand_cgi works with CGI.pm,
 Apache::Request or anything with an appropriate "param" method. Or you
 can use expand_hash directly.
 .
 If you prefer to use a different flattening convention then CGI::Expand
 can be subclassed.