feat: creating new mx_ suite of macros!

also adding new mx_getcode macro

tests/base/mp_jsonout.test.2.sas

@@ -0,0 +1,52 @@
+/**
+  @file
+  @brief Testing mp_jsonout.sas macro with special missings
+
+  <h4> SAS Macros </h4>
+  @li mp_jsonout.sas
+  @li mp_assert.sas
+
+**/
+
+filename webref temp;
+
+data demo;
+  do x=._,.,.a,.b,.c,.d,.e,-99, 0, 1,2, 3.333333;
+    output;
+  end;
+run;
+%mp_jsonout(OPEN,jref=webref)
+%mp_jsonout(OBJ,demo,jref=webref,fmt=N,missing=STRING)
+%mp_jsonout(CLOSE,jref=webref)
+
+data _null_;
+  infile webref;
+  input;
+  putlog _infile_;
+run;
+
+libname web JSON fileref=webref;
+
+/* proc json turns to char - so switch back to numeric */
+data work.test(keep=x);
+  set web.demo(rename=(x=y));
+  if y ='_' then x=._;
+  else if anyalpha(y) then x=input(cats(".",y),best.);
+  else x=input(y,best.);
+  put (_all_)(=);
+run;
+
+%mp_assert(
+  iftrue=(&syscc=0),
+  desc=Checking for error condition with special missing export,
+  outds=work.test_results
+)
+
+proc compare base=work.demo compare=work.test;
+quit;
+
+%mp_assert(
+  iftrue=(&sysinfo=0),
+  desc=Returned json is identical to input table for all special missings,
+  outds=work.test_results
+)