update to the neighbors plugin to retrieve neigbors for categories and subcategories
altered plugin to work with updated subcategory plugin
i18n_subsites plugin: implement jinja2.ext.i18n support

this commit introduces optional support for translatable templates
Merge pull request #142 from alistairmagee/custom_article_urls

Custom article URLs
Merge pull request #141 from alistairmagee/neighbors

Add categories and subcategories support to Neighbors plugin
Minor fixes to Subcategory plugin README
More fixes for Subcategory plugin README
Minor fixes to Custom Article URLs plugin README