Command hierarchy should be reflected in the result table

[giann]

If you define a hierarchy of command it should be organized the same way in the result table.
It would avoid name collision between command names and argument names of subcommands.

local parser = argparse()
    :name "test"

local mainCommand = parser:command "command"
local subcommand = mainCommand:command "subcommand"
subcommand:argument "arg"

lua cmd.lua command subcommand argument

{
    mainCommand = {
        subcommand = {
             arg = "argument"
        }
    }
}