Fixes #221.

In Python 3, `dict.values` returns a dict_values object, which does not support indexing.

>not supported, since they cannot be represented in the node tree.
It's not that they cannot be represented, it's that they would have to be evaluated.

"inherent limitation in wikicode" sounds misleading it's about generating an AST instead of HTML.

Clarify due to #156

2 is dead, long live 3. Mainly turning print info a function
and urllib import fixes

The new version ('core') is much more used and developed
than the previous one ('compat').

This is a breaking change for those who rely on default behavior.