Support start/end dashes in include_template tag

[danieljsummers]

The Liquid templating language specifies that, if a tag starts with {%- or ends with -%}, if there is a line break immediately before or after that tag, it will not be preserved. Currently, the custom include_template tag does not support this, as it's implemented as a regular expression that is replaced when the template is initially read.

Modify the processing for this tag to support the no-new-line options the way other Liquid tags do.