handle sections for arrays

[steve-chavez]

Should be like:

create or replace function hello(xs text[]) returns text as $$
Hello, {{#xs}} {{.}} {{/xs}}
$$ language plmustache;

select hello(ARRAY['a', 'b', 'c']);
Hello a b c

According to https://github.com/mustache/spec/blob/master/specs/sections.yml#L181-L186