Some more file/path restructuring.

All #includes now explicitly use the "<libopencm3/stm32/rcc.h>" format.
If you want to get rid of the "libopencm3" prefix in your local project you
can add a respective -I entry in your Makefile (not recommended though).

All .ld files and .a libs are installed in $(TOOLCHAIN_DIR)/lib
directly (as before), but are now renamed to avoid potential
conflicts now or in the future. Examples:

  libopencm3_lpc13xx.a
  libopencm3_lpc13xx.ld
  libopencm3_stm32.a
  libopencm3_stm32.ld

lib/stm32/adc.c

@@ -31,7 +31,7 @@
  *  reg16 = adc_read(ADC1, ADC_CH_0);
  */
 
-#include <stm32/adc.h>
+#include <libopencm3/stm32/adc.h>
 
 void rcc_set_adc_clk(u32 prescaler)
 {