find attributes in the attributes/ directory if none are specified in metadata.rb file

If no attributes are specified in the metadata.rb file, try to discover them under the attributes/ directory. The algorithm is not perfect but should work in most cases. All three different styles of comments are supported. Examples:

#<> Set user configuration directory.
default[:foo][:user_dir] = nil

=begin
#< 
Set base directory
#>
=end
default[:foo][:base_url] = "/foo/bar"

#<
# Install version.
#>
default[:foo][:version] = "6"

The attributes in the generated documentation appear in the same order as specified in the attribute files.