Fix PipelineExtension.render_individual_css arguments

CompressedCSSNode.render_individual_css accepts **kwargs but
PipelineExtension.render_individual_css does not. This causes an
error when render_individual_css is called with the (unused) kwarg
'templates'.
Update pipeline_settings to support Python 3
Merge pull request #203 from dnerdy/pipeline-extension-render-individual-css-fix

Fix PipelineExtension.render_individual_css arguments