* Enable CXX by default

It's silly not to provide all algorithms by default,
c++ compiler are easy to find these days, worst case it can still be disabled

Also remove lib suffix

* Update doc

* Only compile tests in top-level projects.

* Add an option for building tests.

* Update CMakeLists.txt

* Rely on ciso646 and __cplusplus macro when detecting cxx

* Add CXX11 flag to cmake

* Add a stub for AGS algrithm

* Finish basic integration of AGS

* Clenup ags header, change cmake for test

* AGS: add stop by reaching required value

* AGS: add stop by timer

* AGS: add correct return code for max_time stop

* AGS: stop instead of throwing an exception

* Get rid of unused code

* AGS: use NLOPT_CXX11 macro

* AGS: updated documentation

* AGS: fix wrong ifdef

* AGS: use spaces rather than tabs

* AGS: fix enum name

* AGS: fix wrong calculation of constraints

* AGS: add an example of problem with nonlinear constraints

* AGS: update docs

* Fix minor issues

* AGS: allow up to 10 dimenstions instead of 5

* AGS: fix warnings

* AGS: fix zero evaluations counter, set default maxeval

* AGS: fix generation of test suite

do_multi_index_op has been dropped from Octave 4.4, with a call to
octave::feval being the recommended replacement. See, e.g.
https://hg.savannah.gnu.org/hgweb/octave/rev/c6714ae1c06c

The keyword PREFIX is no longer supported by octave-config and
OCTAVE_HOME is to be used in its stead. See
https://hg.savannah.gnu.org/hgweb/octave/rev/b95c430c0649

Add virtual destructor to class Global, because it has virtual functions.

I specified the language on each relevant code example, so the proper syntax highlighting should be used.

Also I fixed the C++ part, where every angle bracket was escaped with additional quotation marks and thus hiding some relevant information in the online docs.

Also I added a C++ output functionality with `std::setprecision` (from the include `iomanip`) which behaves equivalent to the printf from the C\C++ part.

Was set to 3.0 by #108 altough target_include_directories existed earlier:
https://cmake.org/cmake/help/v2.8.11/cmake.html

* Add nlopt_get_numevals

We reuse stop.nevals which becomes stop.nevals_p, a pointer to opt.numevals, an int that we can return to the user.

* Add doc