Fix over-eager rewrite_hash_links regexp in SSTemplateParser

Copied `SSViewer`'s `rewrite_hash_links` regexp to `SSTemplateParser`. As this is meant to represent the same functionality in two different areas, it should behave the same way in both. Currently it's too eager and activates on all strings matching `href="#`, which messes with things such as the `xlink:href="#sprite-name"` attribute in SVG sprites.