Clean up steady state file examples/NK_baseline_steadystate.m to make it Dynare 4 compatible.

Also shows how to use file to impose restrictions using the check indicator
(cherry picked from commit 1b5641575f0f3e6f22c5d62f386446bdc774b491)
Add example3 that uses steady_state_model block to call fsolve
(cherry picked from commit a0934d0c5716952cff323fe0defb44f47757b281)
Add example files to manuals and describe what they do
(cherry picked from commit c837bce03026626a483f6bfa4b58db0e3d6b2b08)