fix: updating mf_abort param in mf_verifymacvars, also fixing return code as per documentation, adding a test, and updating the header info

tests/crossplatform/mf_verifymacvars.test.sas

@@ -0,0 +1,22 @@
+/**
+  @file
+  @brief Testing mf_verifymacvars macro
+
+  <h4> SAS Macros </h4>
+  @li mf_verifymacvars.sas
+  @li mp_assert.sas
+  @li mp_assertscope.sas
+
+**/
+
+%let var1=x;
+%let var2=y;
+
+%mp_assertscope(SNAPSHOT)
+%mp_assert(
+  iftrue=(%mf_verifymacvars(var1 var2)=1),
+  desc=Checking macvars exist,
+  outds=work.test_results
+)
+%mp_assertscope(COMPARE)
+