The 'root' variable does not exist in current context. Either should call Render(tree) or have it renamed to root. I've chosen root as it's more consistent with the examples later on.
Fixes some tree rendering problems where lines were not properly drawn
at some levels during some circumstances.
* Change the API back to only allow one root.
* Now uses a stack based approach to rendering instead of recursion.
* Removes the need for measuring the whole tree in advance.
Leave this up to each child to render.
Add extension method for specifying horizontal and vertical padding.
Similar constructor for `Padding` already existed.
Update documentation for table column appearance (padding).
Update
`Should_Render_Padded_Object_Correctly_When_Nested_Within_Other_Object`
test to use new extension method.
