Added bzip2 formula

Implementation of bzip2 formula including tests. Passes audit and works on Mac OSX 10.9.4 with latest brew.
@DomT4 do you mean something like this

```
require "fileutils"
.
.
.
FileUtils.mkdir_p man
.
.
.
```

as per this link: http://stackoverflow.com/questions/11463343/does-ruby-have-mkdir-p ?