Use simulation of the model, based on a first order approximation, as
an initial guess for the solver in each period.

NB: the “overwrite” option only works for the same type of “learnt_in” value,
i.e. an integer-valued “learnt_in” cannot replace a date-valued “learnt_in” and
vice versa.

New options {first,last}_simulation_period to perfect_foresight{,with_expectation_errors}_setup commands

[skip ci]

Dates handling inside Dynare statements was done in the Flex scanner using a
hack that would introduce some extra characters in the character stream (in
order to return a call to the “dates('…')” constructor to Bison). But this
would break the column location counter, because the latter would count
characters that do not exist in the user file.

This commit fixes it by implementing a more natural handling of dates, adding
the “dates('…')” constructor directly at the level of the semantic value.

Also do some coding style manual enforcement.

Field names used in the option structure were slightly different depending on
whether the option value was an integer or a date. This is confusing.

This commit aligns the structure field names with the option names. Type
checking can then be done at the MATLAB/Octave level.

– New “heterogeneity_dimension” statement
– New option “heterogeneity” to “var”, “varexo”, “parameters”, “model” and
  “shocks” statements
– New “SUM()” operator in “model” block

See issue #1920

The vector of lower and upper bounds is now provided by
{static,dynamic}_complementarity_conditions.m (which accepts parameters as an
argument, in preparation for the possibility of having parameters in
complementarity conditions).

The index that denotes the reordering of equation residuals (so that the
residual of an equation appears at the index of the endogenous appearing in the
complementarity condition) is now in “M_.{static,dynamic}_mcp_equations_reordering”.

Constraints declared through the ramsey_constraints block are also incorporated
in this new interface (and therefore “M_.ramsey_model_constraints” has been
removed).

The symbol can be either input:
– as ⟂ in UTF-8 (codepoint U+27C2)
– or as _|_ in ASCII

The old syntax using the “mcp” tag is now obsolete, but kept for backward
compatibility.

Closes: #127

Closes: #124

The old name is still accepted, but will trigger a deprecation warning.

dr_block has been removed

NB: does not (yet) works with Occbin regime-specific equations.

Ref. dynare#1890

Incidentally, makes tag names case-insensitive in “model_replace” and
“model_remove”, which is consistent with tag declarations.

Currently defaults to 0.

Those options do not internally behave as the usual command options (which have
a “o_*” rule), so it makes more sense to treat them differently.