Log Message:
py-cparser: updated to 2.20

Version 2.20:
- Fix slow backtracking when parsing strings.
- Parser for FuncDecl incorrectly sets declname attribute on return type.
- Fix crash when file starts with a semicolon.
- Fix array type generation.
- Fix failed parsing of unnamed function parameters with array dim
  qualifiers.
- Fix pointer type generation.
- Fixes for u/l constant integer suffix.
- Fix error transforming an empty switch.
- Recognize integer multicharacter constants like 'ABCD'.
- Fix incorrect AST when parsing offsetof.