make all AST classes sealed to improve error reporting on matching
fix DefUse bug

code introduced match without default case, causing runtime errors in some linux files
check file presence condition with the full feature model (not with approx.fm)

added additional documentation for clarity
introduce debugging options to log the include paths used
set default BDD library to surpress error message
add support for the GNUC extension __128

This is used in never versions of Linux and won't even parse without this fix