Fix header inludes for rjournal_article()

[rcannood]

I implemented a fix for #257. Perhaps you might want to take a look at the implementation -- because I changed a hacky function into something that's even hackier.

Here is a small example: files.zip. The file test_needs_include.Rmd will fail with the current version of rticles and should be solved with this PR.

Also, I changed a rasterised image into a vectorised one.

Hope this helps!
Robrecht

Checklist:

• Update NEWS.

• Add your name to the list of authors Authors@R in DESCRIPTION. You don't need to bump the package version in DESCRIPTION.

Not applicable

• Unless you have done it in any other RStudio's projects before, please sign the individual or corporate contributor agreement for a significant pull request (it is fine not to sign it if a PR is only intended to fix a few typos). You can send the signed copy to jj@rstudio.com.

• Add the journalname_article() function to R/article.R if the output format is simple enough, otherwise create a separate R/journalname_article.R.

• Add the Pandoc LaTeX template inst/rmarkdown/templates/journalname_article/resources/template.tex.

• Add a skeleton article inst/rmarkdown/templates/journalname_article/skeleton/skeleton.Rmd.

• Add a description of the template inst/rmarkdown/templates/journalname_article/template.yaml.

• Please include the document class file (*.cls) if needed, but please do not include standard LaTeX packages (*.sty) that can be downloaded from CTAN. Please keep the number of new files absolutely minimal, and also make examples minimal (e.g., if you need a .bib example, try to only leave one or two bibliography entries in it, and don't include one hundred items in it without using all of them).

• Update Rd and namespace (could be done by devtools::document()).

• Update README with a link to the newly supported journal.

• Add a test to tests/testit/test-formats.R.

[rcannood]

Oops, didn't mean to click that >_>

[yihui]

I think this is a correct fix. As you said, it looks hackish, so I'll see if I can tweak it a little bit. Thank you very much!