Missing link in Filtering.tex

[jhlegarreta]

The lines

ITKSoftwareGuide/SoftwareGuide/Latex/DesignAndFunctionality/Filtering.tex

Lines 118 to 119 in 6cae7a9

	advantage of this construction. (See the Iterators chapter
	in Book 1 for more information.)

refer to a section in the SW Guide without using the \ref command.

I'm wondering whether it was not used because linking to the first book from the second book would not work, or else, it was just a simple oversight.

In the Coding Style chapter (which is part of Book 1), I've used links to sections in only Book 1, so I ignore whether links across books would work well.