CLI semantic grep tool

[kazcw]

I came across this in the wild:

rg -USP 'match\s+.+\s+{\s+Ok\((\w+)\)\s+=>\s+\1.*\s+Err\((\w+)\)\s+=>\s+\2'

and I realized comacro is not far from being usable for that kind of thing (which doesn't need the complexites of hir integration or necessarily the guarantee that it's false-positive free). #7 will be useful for this.