Need to use an optional `package` field;
incase url's that don't put the file in the url.
This commit amends far more than I would have liked to.

working script will;
Remove existing folders named in the sources
Download the packages listed in sources.json
Extracts the above packages
deletes the downloaded package
Merge pull request #157 from Jackbennett/scripts

Getting the build script to a working state