Split support

[clux]

For #53

Usage;

cargo run -- '.' --split '"blah/" + (.metadata.name) + "_" + (.kind | ascii_downcase) + ".yaml"' ./test/deploy.yaml -y

which will use jq shellout with the split arg as the jq query (allowing you to use ANY jq function

and it produces the following files with each document in the blah subfolder:

controller_clusterrole.yaml         controller_deployment.yaml  controller_serviceaccount.yaml
controller_clusterrolebinding.yaml  controller_service.yaml

it does this by parsing into multidocs initially and running jq shellouts for each document so we can get both the key (for the filename) and the value in 2 jq calls (so 2*N shellouts currently), and at the end it would write the files.

it's not super efficient, 8 shellouts, but it only takes .1s with a release build with all serial IO, so if it gets annoying there's plenty of juice to squeeze out of it.

It's also a completely different mode that only happens when you pass --split, and need to fiddle with it some more, but the basic idea works well. Should work for all file formats, and is possibly a nicer step towards refactoring to smarter doc handling (as is it's a bit sprawling and duplicating fns).