Document macro-expansion stage
Add header to IR dumps
Add docstrings to macro.py
Only dump expanded IR if any macros were expanded
Merge pull request #856 from gmarkall/document_macros

Document macro expansion
Fix use of address_of_symbol() / add_symbol().  This fixes crashes under Windows XP, amongst others.
Merge pull request #871 from pitrou/fix_add_symbol

Fix use of address_of_symbol() / add_symbol().  This fixes crashes under...