KT3 Browse System
=================

KnowledgeTree's browse view has been a serious bottleneck in terms of 
performance, and makes extending the system in useful ways (and re-using items)
unnecessarily hard.

To understand this code, you'll need to look at:

 - lib/browse/DocumentCollection.inc.php
 - lib/browse/BrowseColumns.inc.php
 - presentation/.../browse.php
 
Objectives of the refactor:

 - improve code-reuse 
 - make more advanced document-sets possible
 - unify all document-collection logic (where possible).
 
BROWSE VIEW GENERATION
----------------------

Generating a browse view is now done as follows:

 - create a DocumentCollection object
 - add "BrowseColumns" to it.
 - specify (on the collection) which column to sort on.
 - specify any batching that may be required (count, start).
 - execute the query (using generateCollection).
      returns a set of document ids, in order (more info cached internally).
 - for each row, use "getInfo(docid)" to extract the information from the database.
      returns an array with info (more later), and caches this internally.
 - at render-time, call "renderRow(docid)".
 
Internally this does a fair bit more work.  Particularly:

 - each Column can contribute JOINs, WHERE clauses.  _if_ its the sort column,
   it gets asked for an ORDER clause.
 - the system fetches a LOT of information about each batched item - don't do too much.