More everything into the octave namespace

[Carnë Draug]

There's been a lot of stuff moved into the octave namespace.  Sounds
right to me that we move everything somewhere into the octave namespace.
Is that the plan?

If we are heading that way, I'd prefer if it was all done in one go
(upcoming Octave 4.2 release), instead of gradually.  Makes it easier
to have a package that supports both versions, specially if it involves
renaming functions (maintaing a package that supports old and new Octave
versions when such changes happen is a burden.  If I can limit it to
the Octave 4.0 -> 4.2 transition that would be better).

Should we start moving everything into namespaces?  And if so, what
should we leave in the octave namespace, and what goes into nested
namespaces?

The doxygen docs were updated recently so we can have a list of the
current existing classes [1].

Looking forward to start using octave::Array<T>.

Carnë

[1] http://octave.org/doxygen/4.1/annotated.html