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.
Bugfixes in perfect_foresight and global_solve
DOC: perfect foresight functions
Started documentation of perfect foresight.
Merge branch 'perfect_foresight'