{
  "build": {
    "core": "arduino_zero", 
    "cpu": "cortex-m0plus", 
    "extra_flags": "-DARDUINO_SAMD_FEATHER_M0 -DARDUINO_ARCH_SAMD -D__SAMD21G18A__", 
    "f_cpu": "48000000L", 
    "hwids": [
      [
        "0x239A", 
        "0x800B"
      ], 
      [
        "0x239A", 
        "0x000B"
      ]
    ], 
    "ldscript": "flash_with_bootloader.ld", 
    "mcu": "samd21g18a", 
    "usb_product": "Adafruit Feather M0", 
    "variant": "arduino_zero"
  }, 
  "frameworks": [
    "arduino"
  ], 
  "name": "Adafruit Feather M0", 
  "upload": {
    "disable_flushing": true, 
    "maximum_ram_size": 32768, 
    "maximum_size": 262144, 
    "protocol": "sam-ba", 
    "require_upload_port": true, 
    "use_1200bps_touch": true, 
    "wait_for_upload_port": true
  }, 
  "url": "https://www.adafruit.com/product/2772", 
  "vendor": "Adafruit"
}
{
  "build": {
    "core": "adafruit_feather_m0", 
    "cpu": "cortex-m0plus", 
    "extra_flags": "-DARDUINO_SAMD_FEATHER_M0 -DARDUINO_ARCH_SAMD -D__SAMD21G18A__", 
    "f_cpu": "48000000L", 
    "hwids": [
      [
        "0x239A", 
        "0x800B"
      ], 
      [
        "0x239A", 
        "0x000B"
      ]
    ], 
    "ldscript": "flash_with_bootloader.ld", 
    "mcu": "samd21g18a", 
    "usb_product": "Adafruit Feather M0", 
    "variant": "adafruit_feather_m0"
  }, 
  "frameworks": [
    "arduino"
  ], 
  "name": "Adafruit Feather M0", 
  "upload": {
    "disable_flushing": true, 
    "maximum_ram_size": 32768, 
    "maximum_size": 262144, 
    "protocol": "sam-ba", 
    "require_upload_port": true, 
    "use_1200bps_touch": true, 
    "wait_for_upload_port": true
  }, 
  "url": "https://www.adafruit.com/product/2772", 
  "vendor": "Adafruit"
}

Add new core and variant for adafruit_feather_m0
Add new core and variant for adafruit_feather_m0

Issue #2