Also do some coding style manual enforcement.

The call to model_error() would return and lead to an incorrect dereferencing
of the optional<int> rv.

The call to model_error() should have been replaced by a call to error() in
db1f6c29. Then the move to an optional<int> in
46b2c735 introduced the bug.

See https://forum.dynare.org/t/preprocessing-failed-for-specific-mod-file/26705

This information can be computed from MATLAB/Octave. This will facilitate the
introduction of dates in shock sequences.

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.

This should have been removed in commit 2315bdb5.

Ref. dynare#1859

Epilogue variables can have leads/lags when appearing on the RHS of the
epilogue block.

The method VariableNode::maxLagWithDiffsExpanded() was already handling them,
so this commit adapts other methods for consistency.

HANK support: modifies the driver file writing process to introduce a...

See merge request Dynare/preprocessor!108

HANK support: modifies the driver file writing process to introduce a `state_var` field in the `M_.heterogeneity(i)` structure for each heterogeneity dimension `i`

This rule is obviously incorrect (and useless):
– it begins with an unescaped dollar sign, which can only match an end-of-line
  (so it makes no sense to have it at the beginning of the rule)
– it prints to standard output, which is obviously not the intended action

The driver was calling “clear” before “global”, hence clearing local and not
global variables (unless “global” had already been called at scope).

Rather use “clearvars -global”.

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

Uses:
– structured bindings
– std::map::contains and std::map::at
– std::boolalpha and std::noboolalpha

std::fill takes a range that is open on the right bound (i.e. [first, last) and
not [first, last]).