Update README to match all supported families
stm32f1: Add missing peripheral base address for F100
Clarify toolchains and install steps

Including removing the extremely unhelpful DETECT_TOOLCHAIN option.
sync: use matching #ifdefs in source as in header

Fixes github issue #298
stm32f1: Fix RCC CAN defines

Thanks to Марко Краљевић <krasnaya.zvezda@gmail.com>
[f3] add USART_SR_x defines for common status flags

enables the use of usart_get_flag(USARTx, USART_SR_x) on F3 just like on F124

closes #283
Merge remote-tracking branch 'mainline/master'