Function renderTemplate

Renders a template in these steps. See documentation/vcsTemplate.md for more information.

1. expand conditional blocks. this will remove any blocks that do not match their expressions and choose from if / elseif / else block which of them to render
2. expand iterations. this will create new templates for each iteration and re-run the rendering for those blocks
3. render attributes. this will add the attributes to all the blocks not within each blocks