Update docs w.r.t. warning and strictness options. * doc/automake.texi (Strictness): Document that some warnings are turned off by default in `foreign' strictness. (Options): Divide into new sections "Options generalities" and "List of Automake options". Fix typo (colon instead of full stop). Document option precedence (AUTOMAKE_OPTIONS wins over AM_INIT_AUTOMAKE which wins over command line). Also document interactions between options specifying strictness and those specifying warnings.