Bring Piku more in line with PEP 517 for compatability with other python tools

[mraleson]

This was a suggestion on the CircuitPython forums by aivarannamaa:

https://forums.adafruit.com/viewtopic.php?p=910442#p910442

I see that you have used toml-format for storing project metadata. What do you think of making it compatible with PEP-517, so that your conf file would be named pyproject.toml and looked something like:

    [build-system]
    requires = ["piku>=0.1.4"]
    build-backend = "piku.builder"

    [piku.general]
    project = "example"
    piku = "0.1.1"
    circuitpython = "7"

    [piku.dependencies]
    adafruit_apds9960 = "~7"
    adafruit_bmp280 = "~7"
    adafruit_bus_device = "~7"
    adafruit_lis3mdl = "~7"
    adafruit_lsm6ds = "~7"
    adafruit_register = "~7"
    adafruit_sht31d = "~7"
    neopixel = "~7"

This way the users could use the same file for their Black settings etc.

[mraleson]

Closed with 33c88de0eb6cef67f3562dd508df6f512af8114b