Clearly show multi-line items belong to the tree

[epage]

assert_cmd uses predicates for its assertions and sometimes we are asserting on multi-line stdout and the output can be hard to parse, see assert-rs/assert_cmd#121

One idea we are exploring for this in predicates (see assert-rs/predicates-rs#106) is that we indent the entire block o content to the same level, ie under the tree. Ideally the branch would then flow within that indentation to the next item. This would require support from treeline to do.

[softprops]

Thanks for posting. This makes sense to me

[epage]

Just want to check for understanding if you were expecting to go and implement this or if this was a greenlight for me.

[softprops]

Have at it!