Initial perfect foresight file.
Perfect foresight solver for fga models

Complementarities must be constants.
Some cleanup in the perfect foresight solution.
yaml_import can now take a filename argument for recipes
Added fg rbc model.
Changed final condition for perfect foresight simulation.
Perfect foresight fix to deal with unit roots.
Distinguish 2 fgh recipes: fgh1 and fgh2
Bugfixes in perfect_foresight and global_solve
DOC: perfect foresight functions
DOC: added algos section
REF: Renamed dynare notebook example.
Started documentation of perfect foresight.
Merge branch 'perfect_foresight'
Doc updates + notebook for perfect foresight.
Doc update + recipes.
Merge branch 'master' into dev/dolo-recs