Remixed

Here's a remix of your [PubMed XML scraper](http://rpsychologist.com/how-to-download-complete-xml-records-from-pubmed-and-extract-data).

The main function, `pubmed_get` proceeds by incremental downloads of the raw XML data to a batch folder. It does not perform any post-processing, leaving it for other functions.

The code also fixes an issue in the initial code where [the `RetMax` counter is incremented](https://github.com/rpsychologist/PubMed/blob/master/PubMedXML/PubMedXML.r#L43), therefore leading to file downloads of increasing (instead of fixed) size.

To test the remix, set the working directory to `PubMedXML` and try out the following:

```{S}
pubmed_count("FCTC OR 'Framework Convention on Tobacco Control'")
pubmed_get("FCTC OR 'Framework Convention on Tobacco Control'", file = "fctc")
pubmed_journals("pubmed_fctc")
pubmed_years("pubmed_fctc")
pubmed_authors("pubmed_fctc")
pubmed_names("pubmed_fctc")
```

You can also use the `pubmed_edges` function to get an undirected edge list of coauthors in a given PubMed corpus:

![pubmed_fctc_net](https://cloud.githubusercontent.com/assets/322533/3279530/d38179de-f400-11e3-8add-1d99a8da0f9b.png)

The code contains Roxygen2-like documentation, and [this blog post](http://politbistro.hypotheses.org/2217) (in French) explains how the coauthorship network was built.