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

Automatically detected by clang-tidy using performance-for-range-copy check.

If the user did not specify the GlobalInitFile option, use global_init.m in configuration
directory if it exists.

There was some overengineering related to the Hook class.

– under Linux and macOS, use the “dynare” subdirectory of the configuration
  directory specified by the XDG specification
– under Windows, use the “dynare” subdirectory of the Application Data folder

The old location is kept for backward compatibility, with a warning.

In particular, makes clearer the distinction between configuration and
configuration file. The former includes information that is not in the
latter (command-line options.)

[skip ci]

Adapt the code accordingly.

By the way, remove a redundant Cluster{} constructor call.

This is unsafe since the find() method can return a past-the-end iterator,
which should be tested for.

Replace most instances by calls to the std::map::at() method (which throws if
the key is unknown), and which is incidentally more readable.

In particular, use this feature in many loops which feature a special treatment
for the first iteration, using a boolean variable (replacing iterator
manipulation). By the way, also use std::exchange() to simultaneously test the
value of this variable and update it.

Ref. dynare!1843

This is a partial revert of f022f666

Ref. dynare#1748

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

- no longer use pointers
- use pass-by-value when possible
- use range-for loops when possible

Most cases can be handled in C++11 by std::stoi() and std::stod().

For the macroprocessor ArrayMV<T>::print() method, use template
specialization (instead of a lexical_cast to detect between T=int and
T=string).

The latter accepts a std::string as argument.

In C++11, it is no longer necessary to put a space between two consecutive ">".

Performed using modernize-use-nullptr from clang-tidy.

https://clang.llvm.org/extra/clang-tidy/checks/modernize-use-nullptr.html