Replaces the temporary (place holder) Introduction to qdap Vignette with the actual vignette.
build_qdap_vignette(download.html = FALSE)Places the (1) HTML, (2) source, & (3) R code for the
Introduction to qdap Vignette in the user's
R-VERSION/library/qdap/doc.
logical. If TRUE the file will be downloaded
from: http://trinker.github.io/qdap/vignettes/qdap_vignette.html. This