Feature/vignettes premade (closes #1004)

[eddelbuettel]

See #1004 for discussion.

In a nutshell:

• we build vignettes from Rmd "locally", and then
• include them via the LaTeX / Sweave command \includepdf 'as is' into simple wrapper document
• speeds up package build a little
• renders it independent of tooling changes on the vignette side (pinp, rmarkdown, ...)

[codecov-io]

Codecov Report

Merging #1005 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1005   +/-   ##
=======================================
  Coverage   82.45%   82.45%           
=======================================
  Files          63       63           
  Lines        3164     3164           
=======================================
  Hits         2609     2609           
  Misses        555      555

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[eddelbuettel]

@kevinushey I know you already nodded at #1004 but if you have a minute or two this weekend to glance at this I'd appreciate it.