[CPX] custom data types from gap8 to stm32

[matthewoots]

This PR addresses #116
A look at it is as shown below, using an example of sending apriltag detection of corners and pose estimation related data

crazyflie-firmware will need some tweaks, please use https://github.com/matthewoots/crazyflie-firmware/tree/cpx/receive_data and the commit is matthewoots/crazyflie-firmware@9fcb117

Adding @hmllr here too

[matthewoots]

Linking crazyflie-firmware PR here bitcraze/crazyflie-firmware#1245

[ataffanel]

This looks quite good to me. Ideally we would have an actual API to send and receive APP packet without requiring the user to forge a CPX packet. But this example is good to show the current state of things. Let's wait for the STM32 PR bitcraze/crazyflie-firmware#1245 to be ready before merging this PR.

[matthewoots]

The way I handled this is to create a msg.h (or any other name) that handles serialization and deserialization, this can be copied and pasted into crazyflie-firmware and changing defines to omit the serialization portion (since 1. it does not run need to use the pmsis library and 2. does not need to send back the serialized message and 3. unused functions are not allowed), since the most would be that the user send back a response with a simple byte. Hopefully this helps explain to anyone who want to use it (I'll probably add in documentation next time). :))

@ataffanel, moving forward, I agree that there needs to be an API on this.

This looks quite good to me. Ideally we would have an actual API to send and receive APP packet without requiring the user to forge a CPX packet. But this example is good to show the current state of things. Let's wait for the STM32 PR bitcraze/crazyflie-firmware#1245 to be ready before merging this PR.

[matthewoots]

I'll close this first and touch back on this when I have the time