add Category and Section models to Articles app
add management command to migrate Articles to Category FK
add management fields to Section model
migrate utils into their own app directory
add utilities for cached page invalidation
post_save cache invalidation for articles
post_save cache clearing for code, person, organization models
add django_pluralize template filter
add author bios to article detail page
fix id attr for bio h3s
Merge pull request #173 from ryanpitts/authors

author bios on article detail pages
size twitter avatar img to normal 48px
Merge pull request #174 from ryanpitts/authors

size twitter avatar img to normal 48px
fix author box p in case of one-line bio
Merge branch 'authors' into caching
add view to trigger cache clear for path
add homepage cache clear link to admin
add same-origin ajax handling
add ajaxy cache clear link to admin index
remove auto homepage cache clear from article, code saves