feat: adding mddl_xx series of macros (and tests). Closes #166

ddl/mddl_dc_difftable.sas

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+/**
+  @file
+  @brief Difftable DDL
+  @details Used to store changes to tables.  Used by mp_storediffs.sas
+      and mp_stackdiffs.sas
+
+**/
+
+
+%macro mddl_dc_difftable(libds=WORK.DIFFTABLE);
+
+  proc sql;
+  create table &libds(
+      load_ref char(36) label='unique load reference',
+      processed_dttm num format=E8601DT26.6 label='Processed at timestamp',
+      libref char(8) label='Library Reference (8 chars)',
+      dsn char(32) label='Dataset Name (32 chars)',
+      key_hash char(32) label=
+        'MD5 Hash of primary key values (pipe seperated)',
+      move_type char(1) label='Either (A)ppended, (D)eleted or (M)odified',
+      is_pk num label='Is Primary Key Field? (1/0)',
+      is_diff num label=
+        'Did value change? (1/0/-1).  Always -1 for appends and deletes.',
+      tgtvar_type char(1) label='Either (C)haracter or (N)umeric',
+      tgtvar_nm char(32) label='Target variable name (32 chars)',
+      oldval_num num format=best32. label='Old (numeric) value',
+      newval_num num format=best32. label='New (numeric) value',
+      oldval_char char(32765) label='Old (character) value',
+      newval_char char(32765) label='New (character) value',
+    constraint pk_mpe_audit
+      primary key(load_ref,libref,dsn,key_hash,tgtvar_nm)
+  );
+
+%mend mddl_dc_difftable;