Add .onAttach call informing on varname change

Author: Liam Hobby

R/zzz.R

@@ -39,3 +39,7 @@ globalVariables(c("private",
                   "where_new",
                   "var1",
                   "n_lab"))
+
+.onAttach <- function(libname, pkgname) {
+   packageStartupMessage("Attaching package `metacore`\n\nAs of metacore 0.3.0 the `keep` variable in the `ds_vars` table has been renamed to `mandatory`. Please see release documentation for details.")
+}