Rename 'excerpt' to 'blurb' in custom templates

Since excerpt is used elsewhere by Jekyll, and isn't as descriptive of what the text actually is.
Add 4 new placeholder files for in-progess posts

1) Dashdash announcement
2) Social network designed for Glass
3) Conversation on Twitter
4) XMPP/Jabber browser extension for Gchat
Add template support for custom CSS in posts
Add logo & fancy hover screencast to Dashdash post
Add support for images as post titles
Add market-share images & CSS for future reference
Progress on Dashdash post (first half, email form)
Finish first draft of Dashdash post

Re-added the iPhone images, which I think might be good to use after all.

ARGH at Jekyll's Rdiscount Markdown for not supporting multi-block-item footnotes, so that HTML is a mess and impossible to read, and I had some CSS to make it work.
Replace Dashdash sreencast.gif with YouTube video

Sigh, the hover CSS I'm deleting was a bit of a pain to get working, but it was too easy to accidentally load the image and start the screencast. There's too much going on for the reader not to be able to pause, fast-forward, and rewind.
Make final edits before sharing Dashdash post draft
Merge branch 'new_posts'