Added provisions for the section about the model file.

doc/manual/source/the-model-file.rst

doc/manual/source/the-model-file/auxiliary-variables.rst

doc/manual/source/the-model-file/conventions.rst

...anual/source/the-model-file/deterministic-simulations.rst

...l/source/the-model-file/displaying-and-saving-results.rst

doc/manual/source/the-model-file/estimation.rst

doc/manual/source/the-model-file/expressions.rst

doc/manual/source/the-model-file/forecasting.rst

...e/the-model-file/getting-informations-about-the-model.rst

...source/the-model-file/initial-and-terminal-conditions.rst

...anual/source/the-model-file/macro-processing-language.rst

doc/manual/source/the-model-file/markov-switching-sbvar.rst

doc/manual/source/the-model-file/misc-commands.rst

doc/manual/source/the-model-file/model-declaration.rst

doc/manual/source/the-model-file/optimal-policy.rst

...nual/source/the-model-file/other-general-declarations.rst

...manual/source/the-model-file/parameter-initialization.rst

...he-model-file/sensitivity-and-identification-analysis.rst

...l/source/the-model-file/shocks-on-exogenous-variables.rst

doc/manual/source/the-model-file/steady-state.rst