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.

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

Closes: 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 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.

Incidentally, replace the IS_* macros by inline functions.

ensure that trend_variable found is actually a trend variable as declared in the trend_component_model statement

Given a previously declared var_model, the var_expectation_model statement is
used to declare a way of forming expectations with this VAR (possibly using a
finite or infinite discounted sum). The var_expectation operator now takes a
single argument, the name of the var_expectation_model.

For the moment, this only works when the var_model is using equations
explicitly declared in the model block.

See McModelTeam/McModelProject/issues/97.

aux_equations only contain the definition of auxiliary variables, and
may diverge from those in the main model (equations), if other model
transformations applied subsequently. This is not a problem, since
aux_equations is only used for regenerating the values of auxiliaries
given the others.

For example, such a divergence appears when there is an expectation
operator in a ramsey model, see
tests/optimal_policy/nk_ramsey_expectation.mod */

This table serves no useful purpose. It is better to append auxiliary equations
at the time they are created, to avoid messing with the recursive ordering.

Ensure that all diff operators appear once with their argument at current
period (i.e. maxLag=0).
If it is not the case, generate the corresponding expressions.

This is necessary to avoid lags of more than one in the auxiliary
equation, which would then be modified by subsequent transformations
(removing lags > 1), which in turn would break the recursive ordering
of auxiliary equations.

See McModelTeam/McModelProject/issues/95 for an example.