A Macro represents a LogicalFile transformation.

Each Macro is implemented by a module through the apply_macro callback with zero or more arguments in a keyword list.

A 'Macro invocation' is specified as a tuple in the form {module, [options keyword list]}. A macro is called through the apply_macro callback which takes a LogicalFile and returns a possibly transformed LogicalFile.

The macro processor applies macros in turn to a base LogicalFile and each macro is expected to return a valid LogicalFile.

Sample macro implementations are provided for handling file includes (LogicalFile.Macros.Include) and single-line comments (LogicalFile.Macros.LineComment).