Update the CXCursorKind API to 3.0
Make CXCursor compatible with pre- and post-3.0

The CXCursor structure has an extra field in libclang 3.0. This
makes libclangpy use the correct structure on all versions of
libclang.

It is necessary to delay mapping of the varying types, as the
decorators are resolved in the parsing phase.
Update the CXCursor API to 3.0
Update the CXType API to 3.0
Update the CXTranslationUnit API to 3.0
README: update the support status for libclang 3.0