add colour support for R CMD {build,check,INSTALL}

This PR adds colour support for the output of `R CMD {build,check,INSTALL}`:

![maker](https://cloud.githubusercontent.com/assets/1828443/2782233/23476198-cb1d-11e3-8351-7f989019a908.png)

What do you think about it? (of course, you can disable it by setting `COLOURS=0`)