OpenCS 2.1.0 released

The major revision of the OpenCS.

The new version introduces the concept of equation groups and equation kernels.
Kernel equation bring performance improvement of one order of magnitude (in average).

New features:
Models can contain a coupled set of kernel equations and auxiliary equations.
All equations must belong to one of equation groups or kernels.
Auxiliary equations must be placed into a single or multiple groups of equations.
Kernels by default represent a group of equations.
Compute Stack Evaluators now operate on groups of equations (or kernels), not the range of equations.
Kernels generate source code in C++ (shared library kernels) and OpenCL.
The source code for shared library kernels is automatically compiled (CMake-based build).

Known issues:
Kernel OpenCL evaluator and partitioning group-/kernel-based models might not function as expected.