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]).

[skip ci]

Closes: #128

It was previously in case-sensitive alphabetical order (i.e. ASCII order).

Ref. #128

– use std::pair instead of std::tuple in internal storage
– make Environment::getFunction() symmetric with Environment::getVariable()

Ref. #125