Capture whence information in all Serval logging API entry points.
Introduce the LogLevel enum type to avoid exposing internal C API
details in the Swift API.
Rename Swift API methods and types to use camelCase naming style, to
distinguish it from the C API, which uses under_score naming style.
Rename the logging primitive functions and utility functions, prefixing
all with 'serval_log', eg: logMessage() -> serval_logf() etc.
Add an XPRINTF xhexdump() function and use it to implement the
serval_log_hexdump() utility, renamed from dump(). Add macros
WHY_dump(), WARN_dump(), HINT_dump() and DEBUG_dump(), and use them
everywhere.
Remove the 'log.console.dump_config' and 'log.file.dump_config'
configuration options; configuration is now dumped in every log prolog.
The logging system now constructs the log prolog by invoking the new
'log_prolog' trigger, so that it no longer depends on the version string
and configuration system. Any system that wants to present a message in
the log prolog can define its own trigger, which calls standard log
primitives to print the message.
Split the logging system into a front-end (log.c) that provides the
logging primitives and is independent of the configuration system, and a
set of back-end "outputters" (log_output_console.c, log_output_file.c,
log_output_android.c) that may depend on the configuration system and
are decoupled from the front-end using the 'logoutput' link section.
These log outputters are explicitly linked into executables by the
Makefile rules, but could also be linked in using USE_FEATURE(). The
USE_FEATURE() calls have _not_ been added to servald_features.c, so that
different daemon executables can be built with the same feature set but
different log outputs.
