Allow <Include>ing of xml with root different from <Lems>

[pgleeson]

A statement like:

should allow a file with root to be included, the root ignored, and everything inside treated as normal lems components.

This simple extension should allow any type of xml to be imported and using 'root' makes it clear that it's just the top level element that should be ignored (an error can be thrown if the root is different). In future some more complex XPath/XInclude based expression could be used to pick out the appropriate element, but this should not be needed for now.

[robertcannon]

I've made it simpler - it just disregards the enclosing type of what you ask it to include. It means users might do silly things, but I doubt it will be much of a problem.