compare compare_items<T>
handler item_handler<T>
iterators used to iterators sets of journal objects
filters derived from item_handler, they morph the result set
output derived from item_handler, these do the printing
Also, created a new 'help' files which contains just Ledger's help text.
old system (for example, the meaning of 'a') has yet to be restored. In the
new scheme, this will be done by definition a function outside of the value
expression logic, rather than the tight coupling between journal innards and
value expressions that occurred in 2.x.
