Things that need to be done:
* redo the errors to confess
* more features for the SimpleAggregator
* in RowHandle add getTable()
* add the row contents access methods directly on a row handle?
* in Row add the array index argument in get(), a version of get by index
* add get() and friends directly on Rowop
* iteration backwards
* identify a group for iteration by the pair (parent index type, leaf index type)
* an encapsulation of iteration range: begin, end, direction, maybe level of the step, group
* add $unit->makeLabelFrom() - a computational block with input and output labels,
  input chained from another label
* add option fromLabel throughout templates
* change options to capitalized
* add a Sequence template, that calls its multiple output labels in order
* a pseudo-table that keeps only the state of the additive aggregations, without actual data
  (the data just passes through and gets immediately aggregated)
* convert everything to croak on errors (at least, the non-ignorable ones)
* option in labels, tracers etc. to not rethrow the Perl errors but just print them
* replace the exceptions with returning error bufs?
* replace all direct Perl_croak() with a smart stack unroll
* in Table, do something about collapsing empty groups on exception?
* in FIFO index, add options to match on exact or on first, or never match,
  and by default throw an exception
* snapshot queries in small portions (would need a comparison per key)
* should it throw from Unit::clearLabels(), and if called from a destructor, 
  catch it there?
* for basic persistence, add dump of tables, quick disconnect of results on reload
* register error messages from the outside scopes, to be printed on failure in the called functions
* in Tray handle the undefs and NULLs better (see XXX)
* rewrite makeLoop* with a Loop object
* make the Perl tracer with row contents a standard Triceps object
* in the C++-underlying-Perl objects have a place to keep $self,
  with $obj->getSelf()->{CLASS} containing the blessing.
* when printing table types and such, make sure to \-escape the funny characters
* change the XS type checking to confess instead of plain dying
* in Triceps::Fields::makeTranslation take the filter specs as arguments, and the caller's name

* doc: the SQLy way, refer to the filtering example in sc_joins_lookup_manual

App ideas:
* queries on CSV files
* distributed cron
* data cache

