Version export check compares version values for root objects against
export selection and raises warning if mismatched.
Root object nif version, user version and userversion 2 are compared
against all child objects, any mismatch will raise an error.
Merge pull request #166 from Ghostwalker71/export/version_check

Export/version check
Added vertex alpha section and expanded the information for InvMarker
and BSInvMarker
BSX and UPB documentation