R: Vignettes and other documentation

# Vignettes and other documentation

## Vignettes from package 'lme4'

lme4::lmerperf |  | lmer Performance Tips | HTML | source | R code
lme4::lmer |  | Fitting Linear Mixed-Effects Models using lme4 | PDF | source | R code
lme4::PLSvGLS |  | PLS vs GLS for LMMs | PDF | source | R code
lme4::Theory |  | Computational Methods | PDF | source | R code

## Other files in the doc directory

| Doxyfile
| lme4/
| lme4-extras.pdf
| profiling.txt