Provide a warning when detecting the use of an undeclared macro.

[Trevor Moody]

Please can the linter report if an undeclared macro had been used?

Declared macros are considered to be:

• built-in SAS macros such as %scan, %index, %trim, etc
• macros that are already named under the <h4> SAS Macros </h4> section of a job's header
• declared within the job itself (including via <h4> SAS Includes </h4>)

SAS Macro keywords (such as %if,%then, and %do) should not trigger the rule.

It is accepted that macros made available to a job through the SASAUTOS system option will trigger false positives.