Updated links to ST programming manuals
Add a exception handling helper code

This commit add a structure definition that represents the stack frame
layout as it is upon entering exception handler. This is useful when
one wants to alter the exception return address, or get information
about registers state saved by the CPU.
Add a "noreturn" attribute to 'scb_reset_system'

Adding this attribute allows to avoid warnings issued by GCC in cases
when 'scb_reset_system' is used as a last call in a function with
"noreturn" attribute set(usually reset handler of some sorts)
can.c >> bug fixed in receive
CAN2 on STM32F1 is slave and its filter banks are configured thru CAN1 FMR
can speed optimizations
Fixes:
CAN RX: ID conversion was incorrect
Fixed bug with dac_load_data_buffer_dual with register offsets
Place generic USB header and source files into the documentation tree.
Add usb to main index
API change to remove dual loading default case for dac_load_data_buffer_single

Also change dac_data from u32 to u16
Removed examples, they are moved into libopencm3-examples repository.
Using while(1) instead of exit.

The exit function can significantly increase code size, and adds
dependency on stdlibc.
add 16MHz resonator for stm32f4