Add FAQ entry on growing vectors

[eddelbuettel]

New FAQ entry on how (not to) grow vectors

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Prefereably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[eddelbuettel]

There is something wrong between the Rmd or possibly the bib file leading to the render step to bomb out on a tex error -- but I have to run off now to run an errand. Will look into that later.

[codecov]

Codecov Report

Merging #1167 (47fca01) into master (95668a7) will not change coverage.
The diff coverage is n/a.

❗ Current head 47fca01 differs from pull request most recent head 3f2ef89. Consider uploading reports for the commit 3f2ef89 to get more accurate results

@@           Coverage Diff           @@
##           master    #1167   +/-   ##
=======================================
  Coverage   97.44%   97.44%           
=======================================
  Files          64       64           
  Lines        2783     2783           
=======================================
  Hits         2712     2712           
  Misses         71       71           

[eddelbuettel]

Now taken care of -- it was (once again) a bit of brittleness with latex in that _ really does not work in section headers as the table of contents (and alike) processing stumbles.

[Enchufa2]

Oh, I guess you could escape it with a backslash.

[eddelbuettel]

Pandoc does that for you yet it still fails.