Use Babel to format dates

Makes date formatting independent of system locale
Fix for issue #30 - note that this only applies to creating new posts, rebuilding
existing posts does not update their slug separator.
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Merge pull request #28 from lunaryorn/babel-dates

Date formatting depends on current locale
Update CONTRIBUTORS
if app.config.language is None then fall back to English
Merge pull request #33 from takekazuomi/fallbacktoen

if app.config.language is None then fall back to English
Add SimpleHTTPServer-based blog server for local testing. Add a test to verify
the server class is working. Add server to test utilities.
Add serve option to cmdline. Add serve to tests for date and for a folder other
than the blog root.
Bring in changes from the master repository, to include updates from
vladris/master.