– 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.)

There is actually no bug in MinGW. The different behaviour under Windows is
expected, because the implicit conversion there is only to std::wstring.

Previously, the MinGW location was appended multiple times to the PATH
variable, which in some cases would make the variable too long and thus
dysfunctional.

The variable is now initialized once when the worker threads are created.

By the way, move the macOS+Octave environment variable initializations to the
same place, for consistency.

The previous system would spawn as many threads as there are object files to be
compiled (which could lead to hundreds of threads for large block-decomposed
models). This could pose a memory usage problem (even when not just waiting,
threads require memory for their own stack).

use_dll: dynamically limit the number of concurrently running GCC processes to the number of available logical processors

Ref. #41

Currently two threads are used (one for the dynamic MEX, one for the static
MEX). When the sparse representation is implemented, four threads will be used.

Closes: #41

Previously it was set to 1.

Also do the same change for variable defined on the command-line, for
consistency.

Closes: #43

But still accept the old name for backward compatibility.

Closes: #86

This option tells the preprocessor not to use the commutativity of addition and
multiplication when looking for common subexpressions.

As a consequence, when using this option, equations in various outputs (LaTeX,
JSON…) will appear as the user entered them.

There is however a potential performance cost to using this option, yet to be
determined.

Ref. dynare#1788

Ref. dynare!1843

— output Julia files as soon as “language=julia” is passed, independently of
  the value of the “output” option
— drop the “dynamic” and “first” values of the “output” option, since they
  actually do nothing
— obey the “output” option even in the deterministic case

Ref. dynare#1600

This is necessary to avoid an “unknown option” error.

Ref. dynare#1743

Ref. dynare#1743

Closes: #62

Ref. Enteprise/dynare#4

Do not print the total computing time at the end of the driver.

This only concerns the situation when `savemacro` is also passed.

When `linemacro` is passed, the macro expanded .mod file is the same as before

When `linemacro` is not passed, the macro expanded .mod file is equivalent to what it was before when both `noemptylinemacro` and `nolinemacro` were passed.

closes #44
closes #45

Allows for the inclusion/exclusion of a set of equations, specified either on the command line or in a text file.

If the equation has a single endogenous variable on the LHS, then the equation is moved. If not, if the equation has an `endogenous` tag then that variable is removed along with this equation. If not, then an error is thrown.

As a command line argument, `exclude_eqs` can take the form (same syntax for `include_eqs`):
* `exclude_eqs=eq1 to remove all equations declared as `[name=eq1]`
* `exclude_eqs=[eq 1, eq 2]` to remove all equations declared as `[name=eq 1]` or `[name=eq 2]`
* `exclude_eqs=[tagname=X]` to remove all equations declared as `[tagname=X]`
* `exclude_eqs=[tagname=(X, Y)]` to remove all equations declared as `[tagname=X]` or `[tagname=Y]`

When declared in a file, the file should be of the form:
```
eq 1
eq 2
```
to remove all equations declared as `[name=eq 1]` or `[name=eq 2]`.

It should be of the form:
```
tagname=
X
Y
```
to remove all equations declared as `[tagname=X]` or `[tagname=Y]`.

ancillary to this change is the move of `paths` out of the Driver class into an argument to parsing/evaluation #32

Note that there is no equivalent of boost::filesystem::unique_path(), so I
implemented ModFile::unique_path() which does something similar.

— allow “language=matlab” for symmetry (this is the default)
— remove the useless “cuda” and “python” values
— give a more meaningful error message when “output” is used in conjunction
  with “language=matlab”