Semantic for config files

[JLuc]

There are several config files

• book.config : defines the chapters
• a global slacheck.config
• possibly some chapters slacheck.config

BUT as for now, eg pdf_bookmark_style can only be defined in book.config. Possibly other settings also.

Proposition is :

• enable to define pdf_bookmark_style in slacheck.config, both global and chapter scoped.
• Better distinguish the semantics of the config files :
  • book.config is to define any global setting AND the name of the chapters.
  • chapter.config, when present in a subfolder, is related to the current chapter