hmc5883l: improve documentation and sample

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

examples/CMakeLists.txt

-add_executable (compass compass.cxx)
+add_executable (hmc5883l-example hmc5883l.cxx)
 add_executable (groveled groveled.cxx)
 add_executable (grovetemp grovetemp.cxx)
 add_executable (lcm-lcd lcm-lcd.cxx)
 include_directories (${PROJECT_SOURCE_DIR}/src/th02)
 include_directories (${PROJECT_SOURCE_DIR}/src/lsm303)
 
-target_link_libraries (compass hmc5883l ${CMAKE_THREAD_LIBS_INIT})
+target_link_libraries (hmc5883l-example hmc5883l ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (groveled grove ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (grovetemp grove ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (lcm-lcd i2clcd ${CMAKE_THREAD_LIBS_INIT})

examples/compass.cxx → examples/hmc5883l.cxx

 int
 main(int argc, char **argv)
 {
-    // Use i2c device 0 all the time
+//! [Interesting]
     upm::Hmc5883l* compass = new upm::Hmc5883l(0);
     fprintf(stdout, "heading: %f\n", compass->heading());
+//! [Interesting]
 
     return 0;
 }

src/hmc5883l/hmc5883l.h

 /**
  * @brief C++ API for HMC5883l (3-axis digital compass)
  *
- * This file defines the HMC5883l C++ interface for libhmc5883l
+ * The Honeywell [HMC5883L]
+ * (http://www.adafruit.com/datasheets/HMC5883L_3-Axis_Digital_Compass_IC.pdf)
+ * is a 3-axis digital compass. Communication with the HMC5883L is simple and
+ * all done through an I2C interface. Different breakout boards are available,
+ * typically a 3V supply is all that is needed to power the sensor.
  *
  * @snippet hmc5883l.cxx Interesting
- *
+ * @image html hmc5883l.jpeg
  */
 
 class Hmc5883l {