Exec poc

[lucastheisen]

@marwatk , this is poorly implemented but shows the how this could work. For example:

lucas@ltp52s ~/git/pastdev/clconf
$ go run ./cmd/clconf --var '/foo=["bar", "baz"]' --var '/hip=hop' getv /foo --exec-string 'echo "{{getv "/"}}"'
bar
baz

If implemented better, worth it?