Integrate with Temple

[frm]

Temple is a fine DSL for our purposes. We're not currently supporting it but it make be a fine addition to our repertoire.

[gabrielpoca]

I'm re-opening this issue because I don't like the path I was taking with this integration. Temple is a DSL, and it doesn't make sense to treat it as just another templating engine that outputs HTML. Temple could be a more dynamic preprocessor or something more than a preprocessor. For instance, I don't think it makes sense to mix Frontmatter with Temple. Instead, I would like to add a DSL to change metadata in Temple. But because we use Temple as a "function" that takes a string and outputs a string, we can't make that.