Bugfix, model shorthand, state.ini[[1]] from observed data

- The bug occurred when using transform_rates=FALSE for FOMC, DFOP or HS
- Make it possible to use mkinfit("SFO", ...)
- Take initial mean value at time zero for the variable with the highest
  value in the observed data
- Update of vignette/FOCUS_L
- Improve the Makefile to build single vignettes