decouple CDeclUse from the type system to make it optional
better error messages
merge split parse results after parsing into single AST

previously, typechef only performed type checking
if the parser succeeded in all configurations.
this was overly strict. now it proceeds with all
successful results in the corresponding contexts
change pretty printer to include attributes inside structs
wip
quickfix: avoid aborting after first #error encounter

proceed lexing and afterward restrict the feature expressions of all tokens to valid configurations.

 this is an incomplete solution. the lexer should not continue in invalid configurations (e.g. try to expand macros there). a better solution would be to rewrite the feature model as well.
Merge branch 'master' into ldebug
reenable sat-based analysis
add further test cases for double free
fixing: typechecking was not performed before dataflow analysis