add missing \import/\usemodule

[kohlhase]

Often I know the symbols I want to annotate, and just write the \sn and so on as I author documents. But adding the necessary \importmodule and \usemodule directives is quite tedious and disruptive. So it would be great, if I could just call srify on the completed document and it would just act on \sn{foo} just as it would on foo, i.e. add the imports and uses.