c89 compatibility

* Add -Wall and -Wextra, fix lots of warnings

 - remove set but not used variables
 - (void) cast unused function arguments
 - create internal function duplicates for some actually
   deprecated functions, for the f77 files disable
   the deprecation warning completely.
 - add warning flags to travis

Note: some of the maybe-unitialized warnings do not
  show in gcc 7.3.0, but travis seems to use a different one.

This closes #226.

* eliminate internal usage of deprecated apis

* 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