Clingo

* update to clasp version 3.3.2
* fix handling of istop in incmode programs
* fix handling of undefined ** operations
* fix preprocessing of disjunctions with undefined operations
(regression in clingo-5)
* fix segfault during preprocessing
(regression in clingo-5)

* switch to MIT license
* improve compatibility with abstract gringo
* switch build system from scons to cmake
* improve windows compatibility
* make tests and examples python 3 compatible
* bison and re2c are no longer required to build source releases
* update to clasp 3.3.0
* the CLINGOPATH environment variable can be set
to control from where to include files in logic programs
* propagators can add variables while solving now
* refactor interfaces (breaking backward compatibility)
* there is just one solve function now
* in the C API do not pass structs by value to functions
because FFIs of some languages do not support this
* fix cleanup function
* numerous other bugfixes not listed here

* fix thread id to start with one in propagator.undo in lua
* fix version macro in clingo.h
* fix added missing methods to get thread id to model in lua/python
* fix child\_key property in python ast

* update to clasp 3.2.1
* add interface to add variables during propagation
* add interface to inspect ground rules (C/C++ only)
* add experimental interface to access clasp facade (C/C++ only)
* fixed smodels output (--output=smodels)

* cleanup of python and lua API (breaks backwards compatibility)
* added new aspif output format replacing the old smodels format
* added input language support for clasp features
* edge directives to add acyclicity constraints
* project directives for enumeration of projected models
* heuristic directives to steer clasp's search
* added theory atoms to write aggregate like constructs
* added stable C API documented with doxygen
* added experimental C++ API based on C API
* added theory propagator interface to clingo APIs
* added support for compilation with Visual Studio 2015
* improved data structures to reduce memory consumption on typical input
* updated to clasp version 3.2.0 + patches

* fixed bug when creating multiple Control objects
(affects lua only)
* fixed bug when trying to configure more solvers than in portfolio
(affects python only)
* fixed disjoint constraints
* improved build scripts
* added option to keep facts in normal rules