Produces incompatible output when indicator characters appear without quoting

[adamwight]

Issue description

Here are a few example cases where values should have been quoted for maximum compatibility:

Ymlr.document!(%{a: ":foo"}) 
Ymlr.document!(%{a: "foo{{bar}}"}) 
Ymlr.document!(%{a: ":foo{{bar}}"}) 
Ymlr.document!(%{a: " foo "}) 

It seems that Ymlr is quoting as minimally as possible, but this causes issues with common parsers which are not totally robust to edge cases. yamlerl fails to parse documents where the indicator characters aren't quoted (in my case, specifically a scalar like ":{{foo}}").

Link to documentation

I wasn't able to find a section in the spec which says all indicator characters must be quoted, but this is the common practice that I've encountered.

[adamwight]

Okay I found that yamlerl has a more specific constraint: it's specifically :{ at the beginning of a value which causes the error. I'm not sure whether this is valid yaml (in which case it must be quoted by ymrl) or if yamlerl is incorrect in parsing this as syntax.