charon: Add custom logger to daemon

This logger can be used to easily register custom logging instances
using __attribute__((constructor)) benefiting from the global reload
mechanism (with reset of log levels).

Note that this is not intended to be used from plugins, which are loaded
after loggers have already been initialized.

Signed-off-by: Thomas Egerer <thomas.egerer@secunet.com>

src/libcharon/Makefile.am

@@ -8,6 +8,7 @@ attributes/mem_pool.c attributes/mem_pool.h \
 bus/bus.c bus/bus.h \
 bus/listeners/listener.h \
 bus/listeners/logger.h \
+bus/listeners/custom_logger.h \
 bus/listeners/file_logger.c bus/listeners/file_logger.h \
 config/backend_manager.c config/backend_manager.h config/backend.h \
 config/child_cfg.c config/child_cfg.h \