I don't think I have the wherewithal to write this full commit message
right now. Since it should be a long one.
Basically. `+ ` now is the string space concatenation operator because
that is a very common use case. It's essentially the soft-wrap
character.
Also, lines starting with -, +, >, and | will now try to tokenize as
map keys if they do not contain the following space. The motivation
here is numeric map keys. Specifically, +/- are numeric leaders.
To facilitate this change, own-line scalars are now prohibited. So, for
example:
key: -1000
is still fine, but
key:
-1000
is no longer accepted.