Indent submodule

[domluna]

fix #484

indent_submodule

default: false

When set to true, submodule(s) appearing in the same file will be indented.

module A
a = 1

module B
b = 2
module C
c = 3
end
end

d = 4

end

will be formatted to:

module A
a = 1

module B
    b = 2
    module C
        c = 3
    end
end

d = 4

end