Added the ability to hide the theme market for speed.
The market is still enabled by default.
Allow user to set multiple categories on posts
Allow user to set multiple categories on posts
Display multiple categories
Display multiple categories
Add multiple categories
Use BLOG_URL instead of $blog_url

Using $blog_url results by an issue when we navigate through a category page : category tags are pointing on `domain.tld/category/category/name`
Make the post link unique.
Change semicolon to comma

Refers to https://github.com/circa75/dropplets/pull/274#issuecomment-26387331
Change semicolon to comma

Refers to https://github.com/circa75/dropplets/pull/274#issuecomment-26387331
Merge remote-tracking branch 'zessx/patch-categories'

I'm combining some upstream fixes to test them in the context of my own.
Merge remote-tracking branch 'lrobert/feature-optional-market'

Continuing to merge other upstream fixes before testing my own updates.