Add preliminary support for HMC5883L magnetometer and MPL3115A2 altimeter.

Logging only, at this stage.

hmc5883l.h

@@ -0,0 +1,10 @@
+#ifndef __HMC5883L_H
+#define __HMC5883L_H
+
+#include "types.h"
+
+bool hmc5883l_init(void);
+bool hmc5883l_start_sample(void);
+void hmc5883l_write_log(void);
+
+#endif /* __HMC5883L_H */