Add initial STM32F070 support

[jessebraham]

Alright, so I did my best to just duplicate #3 as much as possible with this.

Basically just adds the minimal required support for the STM32F070X6 and STM32F070XB devices. There are in fact hardware differences between the two families (which is why they are represented as separate features), they just have not been reflected in code yet.

If there are any changes to be made please just let me know and I'll be glad to do so 😄

[david-sawatzke]

Looks fine to me otherwise

[david-sawatzke]

You'll likely want to wait until #6 is merged for the serial ports.
(Probably for i2c and spi as wel)

[jessebraham]

Awesome, thanks for taking the time to look it over. I can get the timer issue resolved later today, and I'll take a look at #6 and attempt make the appropriate changes to Serial and take a swing at I2C/SPI as well.

[jessebraham]

Okay, first off I merged in #6 from master just to get my branch current. I then made the modifications to the 3 Timers @david-sawatzke pointed out, removing support for the STM32F070X6 devices. I then re-implemented Serial using the new methods merged in from master.

Please let me know if anybody spots any discrepancies. Once the above has been approved I intend to implement I2C and SPI as well; should those be in the same pull request or should we merge this first and create a separate pull request?

[therealprof]

LGTM, thank you!