pyhelper: Add ability to route error messages to python logging

Instead of writing error messages to stderr, route them into the
python code and use the standard python logging system.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/pyhelper.h

@@ -3,6 +3,8 @@
 
 double get_time(void);
 struct timespec fill_time(double time);
+void set_python_logging_callback(void (*func)(const char *));
+void errorf(const char *fmt, ...) __attribute__ ((format (printf, 1, 2)));
 void report_errno(char *where, int rc);
 char *dump_string(char *outbuf, int outbuf_size, char *inbuf, int inbuf_size);