For the IntSequence class, the initialization with {} and () are no longer
equivalent.

We now use a initializer list constructor for creating symmetries of the form
$y^n$, $y^n u^m$, $y^nu^m\sigma^k$.

The constructor taking a single integer is used to initialize a symmetry of a
given length.

Similar changes are made to IntSequence.

This behavior is similar to std::vector.

The former default was 2 threads, since Dynare++ was written at a time when
hyper-threading was being generalized (but multiple cores were not).

On Windows, this means that a POSIX threads implementation is no longer needed,
since C++11 threads are implemented using native Windows threads.

On GNU/Linux and macOS, POSIX threads are still used under the hood.

A new m4 macro (AX_CXX11_THREAD) is used to add the proper compilation
flags (instead of AX_PTHREAD).

- Remove the GeneralMatrix(const ConstVector &) constructor, since it is hides
  a memory allocation (copying the ConstVector into a fresh Vector). This
  helped detecting and fixing several unneeded memory allocations. Some other
  memory allocations are now more visible (with an explicit Vector{}
  constructor).

- Add checks in GeneralMatrix(Vector, …) and ConstGeneralMatrix(ConstVector, …)
  constructors for verifying that the {Const,}Vector has unit-stride (this was
  an implicit assumption so far) and is large enough for storing rows*cols
  elements.

- Add GeneralMatrix::operator=(const ConstGeneralMatrix &).

- Delete ConstGeneralMatrix::operator=().

- these classes now encapsulate a std::shared_ptr<{const, }double>, so that
  they do not perform memory management, and several {Const,}Vector instances
  can transparently share the same underlying data

- make converting constructor from ConstVector to Vector explicit, since that
  entails memory allocation (but the reverse conversion is almost costless, so
  keep it implicit); do the same for GeneralMatrix/ConstGeneralMatrix,
  TwoDMatrix/ConstTwoDMatrix

- remove the constructors that were extracting a row/column from a matrix, and
  replace them by getRow() and getCol() methods on {Const,}GeneralMatrix

- rename and change the API of the complex version Vector::add(), so that it is
  explicit that it deals with complex numbers

- add constructors that take a MATLAB mxArray

By the way apply Dynare C++ coding style and extensions (.cc/.hh).

By the way apply Dynare C++ coding style and extensions (.cc/.hh).

Re Dynare/dynare#1490.

Incidentally, fix a memory leak related to DynamicModelAC instantiation, using
a std::unique_ptr (see Dynare/dynare#1490).

Adapt the k-order DLL as a consequence.

The bug would show at order 3 when the last output argument (derivs) is not
requested (in practice every 3rd order solution without pruning). The DLL would
still attempt to write into it, causing an invalid memory access.

- M and MEX files are now under +${MODELNAME}/
- bytecode, C source and JSON now under ${MODELNAME}/model/

closes issue #1250

In the case where a 2nd/3rd derivative is symbolically not zero but numerically
zero at the evaluation point, the last lines of the g2/g3 matrices (in
KordpDynare::calcDerivativesAtSteady()) where uninitialized (these matrices
store the sparse hessian/3rd-deriv in coordinate list form, i.e. with 3 columns
and as many rows as non-zero elements). When reconstructing the dense
hessian/3rd-deriv matrix out of g2/g3, this would result in invalid memory
accesses.

If the MEX file was called with options_.qz_criterium=[], it would not use a
correct default value (but would use NaN).

Closes #574

Replace them by equivalents in M_ (and an extra one: M_.dynamic).

IMPORTANT POINT: oo_.dr.npred used to count both purely backward and mixed/both
variables. This was the cause of lots of confusion. The new M_.npred only
counts purely backward variables.

We now have the following indentities:

M_.npred + M_.nboth + M_.nfwrd + M_.nstatic = M_.endo_nbr
M_.nspred = M_.npred + M_.nboth
M_.nsfwrd = M_.nfwrd + M_.nboth
M_.ndynamic = M_.npred + M_.nboth + M_.nfwrd

MEX function

Closes: #235

new correction for steady_state operator bug. Steady_state vector is passed as argument to *_dynamic model function. As a result, bytecode is currently broken.

K-order DLL: add test for NaN/Inf in param/steady-state vectors to avoid crashes (thanks to J. Pfeifer for reporting this)