Check out the Kickstarter for the HCC Module!
An easy to solder Arduino and CircuitPython compatible surface mount module aimed to bridge the gap between using "off the shelf" microcontrollers to creating custom PCBs. The module will come with a standard USB enabled Arduino bootloader.
Inside of the folder "BOOTLOADER" there is a folder called "IdleHandsDev". Once you download or clone the repo, take the IdleHandsDev folder and place it in the "hardware" folder found within your default Arduino folder. This will allow you to select the HCC Module in the Arduino IDE. You can also use "Arduino/Genuino Zero (Native USB). It will have the same pinout.