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

Automatically detected using clang-tidy with bugprone-reserved-identifier
check.

By the way, homogeneize the define identifiers in relation to camel case
convention.

Also improve the naming of the enum class used for identifying the type of
external function call.

– a generic one: CommonEnums.hh
– and a bytecode-specific one: Bytecode.hh

By the way, rename global constant “near_zero” into “power_deriv_near_zero”,
for clarity.