do not substitute unary ops in equations that don’t need it (non var_model and non trend_component_model)

It is therefore now possible to write:

  static_model = static_cast<StaticModel>(dynamic_model);

Since, in this case, there are less equations than endogenous, the
variable_reordered structure was not filled with enough element, leading to an
invalid memory read when printing M_.state_var.

Ref #637

Introducing a new DataTree::getVariable() const method was necessary in the process.

In particular, it is necessary to turn back DataTree::AddVariable() into a
non-virtual method, because it is called from DataTree's constructor. Enforcing
the absence of leads/lags is now done using a new boolean DataTree::is_static.

Take advantage of the new copy constructor for handling
PlannerObjectiveStatement more elegantly.

Unfortunately it is not possible to implement *move* constructor / assigment
operators, because the reference ExprNode::datatree is not mutable.

This facilitates switching variable types on the fly. In particular, this
allows removing the hack in DynamicModel::updateAfterVariableChange() that way
basically recreating all the nodes after the type change.

Commit c6cb9aa1 was not the right fix.

The syntax makes clearer the distinction between a function call and an
initialization. Also, it prevents bugs due to implicit type conversions.

For a rationale, see http://www.sjbrown.co.uk/2004/05/01/always-use-explicit/

The check is done at the time the preprocessor is compiled, but it ought to be
done at the time when the C source file generated by the preprocessor is compiled…

Anyways, it is probably irrelevant now, since MSVC has supported
acosh/asinh/atanh for a long time now.

This was not conceptually an enum, but rather a collection of unrelated
constants:
- two constants for use as placeholder for symbol IDs at different places
- one constant for the default number of arguments

Closes: Dynare/dynare#1315

This mimicks the structure of M-functions (though the logic for filling the
temporary terms vector is a bit different).

This change implied a modification in the way we compute the checksum in case
of block decomposition (the temporary terms for the C output are not correctly
computed in that case).

Adds a new model option "linear_decomposition" that creates a block composed of…

See merge request !1

Adds a new model option "linear_decomposition" that creates a block composed of the non-linear equations o the model

Since model local variables are now treated as temporary terms, they must be
marked as such even when option notmpterms is present.

Due to a limitation of the current implementation, this breaks syntaxes like
[ (i,j) ] (but not [ (2,j) ]; the problem only occurs when an array is
constructed by specifying as first element a tuple whose first element is a
variable name). Solving this problem requires an overhaul of the
macro-processor, with construction of ASTs at parsing time, and evaluation
later on (instead of doing on-the-fly evaluation).

Ref #5