R graphics

## Overview

Part of this suite of tools generates a formatted CSV file with statistics about a git repository. The aim of this pull request is to introduce code for processing that CSV data and producing informative data graphics that show:

- Commit activity over time
- Additions and deletions to files over time

### Commit Activity Summary Plot
![CommitActivityOverTime-1](https://f.cloud.github.com/assets/330036/130325/80a3c67a-7014-11e2-8088-eb696e35fd51.png)

### Small multiple summary of per-file additions and deletions
![Small Multiple Summary](https://f.cloud.github.com/assets/330036/130328/a10e761c-7014-11e2-8de2-53d293812b07.png)