overhauled documentation

includes minor refactoring in example code and modification of how the
generic and the tinygecko specific vector.h go together (bringing it in
line with stm32/f1's memorymap.h)

lib/efm32/tinygecko/vector.c

@@ -18,7 +18,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#include <libopencm3/efm32/tinygecko/vector.h>
+#include <libopencm3/efm32/vector.h>
 
 #define WEAK __attribute__ ((weak))