R 3.1.0, support for saving a plot created via the ggplot2 library

My first pull request, apologies if I've done anything incorrectly, also I just noticed you've been making some changes to the development branch so it could be the issues I was running into have been corrected by now.

By motivation for creating the R-3.1.0 branch was to get the ggplot2 package working correctly, specifically ggsave was failing for me.  I probably made too many extraneous changes in the process of getting this going, but figured I would create a pull request, and if there is anything that is useful for you to pull into the main branch, great, if not, no worries.

So a summary of the changes I made:
## /support 
* removed the old vulcan build files.
* removed the auto-upload to S3 (it tended to time out on me).
* changed how the source files and versions are specified, split this out into build-r.config, so that at least in theory version / source location changes don't require changing the actual build script.
* changed where source files are downloaded to, they now get put in /support/sources.
* copied the output of the build to /support/sources.
* added an unpack helper function which only unpacks the downloaded zip files if they haven't already been unzipped.
* altered the build-r file some, modelling more closely on the old R 2.15.1 version of the script as I was able to run ggsave with this version of the build script.
* updated the readme adding a bit more detail.

## /test
* added a test for ggplot.
* added a readme file. 
* updated the install files to source the buildpack URL from a config file, test.config.

## /bin
* made the configurable section of the compile file more obvious.
* removed the tokenized build URL and instead specified it directly (I found this less error prone, I was forever typing in the wrong buildpack version number).