Vignettes to-do list:
[x] filtering returned parameters from $draws()
Showcase how one can read in only selected parameters.
[x] variational inference (done in #210)
[x] optimization (done in #210)
[x] profiling (done in #435)
[ ] standalone generate_quantities
[x] vignette on how to use different draws formats
[ ] example with changing adapt delta and max_treedepth
[ ] Installation vignette
[ ] threading vignette
[x] OpenCL vignette
[ ] MPI vignette