Allow declaration block in the ast-cc source

[eryjus]

The ast-cc source code needs a copy block similar to that of flex or bison.

• [x] Add the copy block to the parser file.
• [x] Update the code generation to emit the block.
• [x] Update the documentation to reflect the changes.
• [x] Update the sample files accordingly.

[eryjus]

This has been incorporated into v0.1.