Bump version to 0.5.0

Major changes
 - fix locale handling
 - fix note URLs
 - fix page redirections
 - fix daily RSS browsing
 - fix title display
 - fix links not being hidden when `HIDE_PUBLIC_LINKS` is set
 - restore compatibility with PHP 5.3
 - remove duplicate tags in links
 - remove annoying URL patterns
 - add Firefox Social API
 - Search/Filter by tag fieds can now be accessed quickly with the `Tab` key
 - update documentation
 - start code refactoring
   - move all settings to `data/config.php`
   - refactor Config, LinkDB, TimeZone, Utils
   - add unit test coverage
   - add Travis integration

Signed-off-by: VirtualTam <virtualtam@flibidi.net>