Add simpler routines for attribute set/get

[raovgarimella]

User requested that we have simpler routine for setting or getting attributes. Currently, one uses the syntax
MEnt_Get_AttVal(mentity, attrib, &ival, &rval, &pval);
MEnt_Set_AttVal(mentity, attrib, ival, rval, pval);
User wants
MEnt_Get_AttVal_Int(mentity, attrib, &ival);
MEnt_Set_AttVal_Int(mentity, attrib, ival);
MEnt_Get_AttVal_Dbl(mentiy, attrib, &rval);
MEnt_Set_AttVal_Dbl(mentity, attrib, rval);
MEnt_Get_AttVal_Vec(mentity, attrib, &ncomp, rvalarr);
MEnt_Set_AttVal_Vec(mentity, attrib, ncomp, rvalarr);
MEnt_Get_AttVal_Tns(mentity, attrib, &ncomp, rvalarr);
MEnt_Set_AttVal_Tns(mentity, attrib, ncomp, rvalarr);
MEnt_Get_AttVal_Ptr(mentity, attrib, &pval);
MEnt_Set_AttVal_Ptr(mentity, attrib, pval);