Add basic blog, and two blog posts

[mattstibbs]

I've added two new blog posts which could be published on the site. They're in a new folder _posts/blog

• What is a pitch, and who should do it?
• 9 tips for awesome pitches

This pull request doesn't deal with any of the other Jekyll templating stuff

[mattstibbs]

I've now added a basic blog section to the site, pilfering most of the stuff from the existing pages.

It could do with a bit of style tweaking, but would probably do for getting something up in time for Cardiff.

[DeckOfPandas]

Thanks @mattstibbs

I'm happy with this, so next person who agrees can merge?

[DeckOfPandas]

I'm going to merge this, given that both me and @mattstibbs think it's okay

A few more styling/layout updates to come