CodeSnip Old Code (SVN)

Rationalised how page structures recorded in TSnippetPageStructures are accessed:
* Changed Pages property to be a default indexed array property.
* Added enumerator that enumerates each TSnippetPageStructure contained in Pages property.
* Deleted PageStructure method: function taken by revised Pages property.
Updated calling code re these changes.

Two new units that enable content of snippet HTML pages to be customised. USnippetPageStructure manages the page structure and USnippetPageHTML renders the HTML needed to display pages according to that structure.