DLM documentation

[mgalloy]

There should be a mechanism for adding comments for a DLM. This should allow for output documentation that looks similar to normal IDL code (but marked as DLM, of course), documenting params, keywords, return values, etc.

[mgalloy]

DLM documentation added in r550 and later commits.

[mgalloy]

Comment headers can be added to document the routines using the same notation as a normal header except the comment character is # instead of ;.