Fix some problems in drawing chain...

 - Temporarily removed concept of drawing 'normal' and default escape sequences
   because it's going to be improved somewhat soon
 - Fix tests and example to use more limited formatting API (i.e. only calls)
 - Made a NullPlaceholder that renders no format stuff, as it seemed more
   symmetrical than having the NullSpec thing have a random populate method...
 - Add and end-to-end test to work out draw-chain bug
Implement a stack for escape sequences...

so that we can 'undo' the application of escape sequences heirarchically.
Fix default_formatting example exception...

When used as a default_format, the bool cast caused by simply doing a 'default
or default' was causing an exception because of the implicit use of __len__
Make basic default_formats work again...

Now can use a single Root.format.<name> as a default_format on an element