Code blocks should be able to have default language set

[Ferada]

3bmd apparently has the *code-blocks-default-colorize* setting to supply a default language to use for code blocks. It would be great if we can set this from the meta data of a post (or even the global blog settings?). The same would also apply to other settings - I'd even say that having some place to include custom code would be nice, e.g. in the blog settings and in the post meta data.

The other option I see would be modifying 3bmd with additional syntax to set variables, but that seems messier and less general.

[Ferada]

I'm proposing Ferada@5b20c4d, or a variant of it. It's at the moment not how I'd ideally want to write it, specifically I'd rather use let: name value and also collect multiple lines into a list of bindings, rather than having to squeeze all of it into a single line.

Also, I haven't found a good justification for running completely arbitrary code, so I left that part out for now.

[libre-man]

Would it be an idea to change the metadata parser to implement white space sensitive newlines?
So that

tags: foo, bar, next
    fooz, baz

would be parsed the same way tags: foo, bar, next, fooz, baz would be parsed. I would propose that using four spaces to indent a line would be mean it is a continuation of the previous and that trailing comma's are not necessary, but should be possible.

[libre-man]

So I made a little proof of concept (libre-man/coleslaw@7cdd3e2) for parsing multiple-lines. The indentation is configurable and everything seems to work. If we would combine this with Ferada's commit we would be almost done with this feature if I'm not mistaking.

[Ferada]

I'd rather have "one or more whitespace characters" as a condition for continuation lines, otherwise that seems sensible. If you really want that configurable maybe just specify that condition with a regex instead.