Improve performance

[tfausak]

This will fix #81. It's still a work in progress.

• This removes almost all dependencies. That means no more Hakyll on Pandoc.
• I wasn't able to remove all non-boot dependencies. It would be possible to avoid cmark by writing the issues in HTML, but I don't think that's worth it. Both text and cmark build pretty quickly.
• To avoid pulling in a YAML parser I switched from YAML front matter to an HTML comment. That's why all the content/issues/*.markdown files changed.
• I rolled my own (probably terrible) template engine. It only supports simple substitutions delimited by dollar signs.
• I haven't sanity checked the output for good Unicode support, smart quotes, and stuff like that.
• The Atom and XML feeds don't exist yet.
• The actual code is pretty gross. It's a first pass.

In spite of all that, it appears to work and builds super fast. We'll see what CI says.

[tfausak]

Less than 10 minutes from scratch isn't too bad. That includes installing GHC.

[tfausak]

Hmm, 4 minutes with a warm cache isn't quite as good as I was expecting. None of the groups of lines in the build log have a time higher than 20 seconds, so it must be restoring the cache or something. I think that Travis has images for GHC 7.8; if I was able to use that I might get even better build times.

[tfausak]

I think 2 minutes with a warm cache is about as good as it gets. That's how long a Jekyll build takes. Overall I think this is ready to go. It takes a cold cache build from more than 50 minutes to about 10 minutes; a warm cache from 8 minutes to 2.

I made a couple changes to the output, but by and large everything should be the same. Obviously my home grown static site generator doesn't have as many features as Hakyll, but it was surprisingly easy to put together. The flow for making new issues hasn't changed at all, so that's good.

[jgm]

I rolled my own (probably terrible) template engine. It only supports simple substitutions delimited by dollar signs.

Why not use doctemplates, pandoc's templating engine, which is available as a separate package?

[tfausak]

I didn't know about doctemplates! It looks like the good version of what I ended up with. I'm sure building it is fast enough, but I ended up with only two dependencies (cmark and text). Depending on doctemplates would drag in at least 7 (non-builtin) dependencies.

I think if I was going to bring a templating package in, it would probably be template. But what I've got works pretty well for now.