toolcontext: add a new category for warnings: advices.

Signed-off-by: Jean Privat <jean@pryen.org>
modelize: useless-visibility is an advice

Signed-off-by: Jean Privat <jean@pryen.org>
modelize: useless attribute type is an advice

Signed-off-by: Jean Privat <jean@pryen.org>
modelize: advice on missing documentation

Signed-off-by: Jean Privat <jean@pryen.org>
modelize: advice on useless empty init

Signed-off-by: Jean Privat <jean@pryen.org>
scope: advice for unread local variables

Signed-off-by: Jean Privat <jean@pryen.org>
tests: update sav for changed loop-warning message

Signed-off-by: Jean Privat <jean@pryen.org>
vim: activate -W for syntactic

Signed-off-by: Jean Privat <jean@pryen.org>