New features + template for Sublime Text Spacegray theme

I wanted to create a template for Sublime Text's Spacegray theme (http://kkga.github.io/spacegray/) but in order to make it work I had to add the following features to the builder script:
* a function for converting rgb arrays to hex strings
* the ability to have .erb templates in recursive folders and keep the same folder structure in the output
* the ability to place the scheme name not only at the start of the generated file name, by using a placehoder in the template's file name
* copying additional files that might come with a template (image files for example) over to the output folder