Initial pass at a blogging framework.

Still needs more work on the template used for rendering blog posts,
adding "next" and "prev" links, niceties like an RSS feed, tag cloud,
post listing, ...  someone wanting to learn about Hakyll should do
that stuff, hint hint.
update instructions re: tutorial titles
missed removal of arrow tutorial title
fix computation of build directory paths

Not sure how I got away without running into this bug sooner.
added blog link, and tags
added rss feed
rename blog.html to blog/index.html
added palette posts
Merge branch 'blog' of https://github.com/diagrams/diagrams-doc into blog

merge with remote
fixed templates for index
have travis install palette

When palette is on Hackage, we can move from it from HEAD_DEPS to EXTRA_DEPS_PRE
Add palette to build.sh
build.sh: inline commands to build and run Shake
change /blog/index.html to /blob/
Merge pull request #43 from diagrams/blog

Blog