TIP: use svglite as device in for producing plots in R/ESS code blocks

[Cook, Malcolm]

I wanted to use svglite as the driver for producing .svg plots within org.

It took a little poking around but the solution was one line:

```
(setf (alist-get  :svg org-babel-R-graphics-devices   ) '("svglite" "file"))
```

Of course it requires:

```
library(svglite)
```

...to have been called in the R session.

This greatly simplifies using org to author graphics heavy literate programming 
/ exploratory data analyses, especially in combination with
 -  
https://emacs.stackexchange.com/questions/29871/how-to-embed-svg-output-of-org-mode-src-block-as-inline-svg-in-html-export
 
 - building emacs with svg support

I mention this TIP in case anyone else is similarly inclined, and in case they 
have additional TIPs that similarly improve working with org/ESS/R/svg

Oh, and, you can set it back with:

```
(setf (alist-get  :svg org-babel-R-graphics-devices   ) '("svg" "file"))
```

... and there is probably some juju to make it buffer local 😉

Cheers,

Malcolm Cook