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.
include link to Colligens in readme
reenable error reporting for parser

accidentially disabled with commit c6ccb565bbcb47ae0c309383dff1cd89d6384b9a
Merge branch 'master' of github.com:ckaestne/TypeChef