Add "headtails" vignette

[dieghernan]

Fix #20 This PR adds a vignette to the package. I used knitr, and also rmarkdown has been added. The configuration was done by usethis::use_vignette() (https://usethis.r-lib.org/reference/use_vignette.html, @hadley).

Please let me know if this work matches your expectations.

A number of checks (not included in the PR) have been performed

• Installation on PC Windows 10, vignette works well
• Checked on travis (devel, release, oldrel), appveyor and devtools::check(), no fails
  • https://travis-ci.org/github/dieghernan/classInt/builds/667773863
  • https://ci.appveyor.com/project/dieghernan/classint
• Previews:
  • Rpubs: https://rpubs.com/dieghernan/headtailsvignette
  • pkgdown: https://dieghernan.github.io/classInt/articles/headtailsR.html

Regards

[dieghernan]

I forgot to add this,

• The source package classInt_0.4-3.tar.gz is 136KB on my computer.
• After installed, total size of the doc/ folder is 256KB

Regards

[rsbivand]

OK, thanks. Maybe the built size can be moderated by combining images, but this may be handled later when closer to CRAN submission.

[rsbivand]

Most of the added bulk is in the JS in the HTML file, I think. This is typical of rmarkdown, I'm afraid. Rendering to PDF with knit is about the same size. Since it is informative, I don't think it is a problem, but thanks for noticing and mentioning this.

[dieghernan]

Thank you, regards

[rsbivand]

classInt on CRAN, thanks very much for your contribution! We can refine the vignette later if need be.

[dieghernan]

My pleasure, thanks to you for all your contributions to the R community

[rsbivand]

... already deployed in tmap https://github.com/mtennekes/tmap/issues/406#issuecomment-610830460