Add --build-type=XXX to configure script.
Rename tracker to identifier.

The identifier controls the management of the 64-bit event ID space. We will
use the name "tracker" later on for a different type of actor.
Remove now obsolete inhale script.
Fix division-by-zero bug.

This fixes the hanging described in #59, but the query still returns 0 results
and the partition complains about not finding indexers. Investigating now...
Fix suppressed relay of query to in-memory indexer.

Because loading a bitmap indexer performed a check of the corresponding path on
disk, a partition would report non-existant indexers if they haven't been
flushed. With this fix, a partition now relays the query predicate to
not-yet-flushed indexers.

Relates #59.
Do not send all-zero hits to query.
Add missing comparison predicate.
Make util::range_map serializable.
Fix bug preventing reuse of existing event ID.
Make segments an implementation detail of the archive.

We got rid of segments as they existed before. A segment used to be a sequence
of chunks, and the archive would relay entire queries to a query. The archive
now simply sends out chunks, which are much smaller and allow the query to
quicker get to the requested events. Internally, the archive still keeps a
sequence of chunks but the notion of "segment" is now an implementation detail
and no longer something users need to be aware of.

This change was necessary because the archive keeps a buffer of chunks until
they reach a certain maximum size. Then the archive would flush the chunk
sequence. But when requesting events from buffered chunks, the archive would
return with an "unknown segment" error for the request ID, because it has not
yet been registered. Now an archive lookup first goes through the list of
buffered chunks, and then hits the existing index structure to find the right
chunk. This fixes #59.

Moreover, we made the archive order-agnostic so that it can handle chunks
arriving out of order. This is an important preparation for making the whole
system more distributed, e.g., with multiple receivers, multiple importers,
multiple archives, etc.