Dynamic blocks and meta tags filtering

[Andrew-Morozko]

Resolves #142

Deviations from the spec:

dynamic is not an attribute on a block, but a container block:

document "test-doc" {
	dynamic {
		items = ["a", "b", "c"]
		content text {
			value = "{{.vars.dynamic_item_index}}: {{.vars.dynamic_item}}"
		}
	}
}

dynamic_condition is dropped, content blocks and sections can be conditionally included by using is_included attribute.

There were a lot of corner cases in implementing this, @traut please check out the tests file and make sure that this is expected behaviour.

Dynamic blocks can contain multiple section and content blocks and can be contained by document and section blocks. They are transparently replaced by the children they're instantiating.

Resolves #99

Deviations from the spec:
I named CLI argument in plural (--with-meta-tags)

[traut]

@Andrew-Morozko awesome work here, and that's a great unit-test coverage, thank you! All of the behaviours there make sense to me.

One question I had -- what is the order of evaluation when both items and condition are defined (like here)? Maybe having it as another test case, that combines multi-item items and a condition, would make sense too.

[Andrew-Morozko]

what is the order of evaluation when both items and condition

In spec, condition determines whether or not dynamic item is shown at all, so it is always evaluated first.

On the second thought, if it would be evaluated per dynamic item it would be a bit more more powerful, allowing to selectively hide only some dynamic items. Currently this could be done with by filtering within query_jq.

Although if it evaluated after items, it would loose access to parent's dynamic_var_val... Perhaps they should be evaluated in the order of their definition, allowing user to choose? What are your thoughts?

[anasmuhmd]

LGTM, Thank you @Andrew-Morozko