create iris-deprecated and iris-staging packages, and deprecate some hard-to-use logic-level wrappers as well as view shift and Hoare triple notation

BSD's find adds an extra / when invoked on tests/, and this confuses the
test dependency management.

Fixes #345

var=foo is a "recursive variable assignment", which is expanded on every
use (including re-running shell commands). What we really want is
var:=foo, which is expanded at definition time.