Scripted version of Texas X2QFN-12 (replaces #1221)

Replaces #1221 Needed for https://github.com/KiCad/kicad-symbols/pull/1336

http://www.ti.com/lit/ml/mpqf391c/mpqf391c.pdf

The scripted version has slightly larger toe fillets (towards outside of the package) Heel reduction is used to get enough clearance on the inside. (Set it up such that we have 0.2mm clearance between horizontal and vertical pads. This agrees with the pads given by TI)

Script PR: https://github.com/pointhi/kicad-footprint-generator/pull/250

Texas_X2QFN-12_1.6x1.6mm_P0.4mm:
  device_type: 'X2QFN'
  manufacturer: 'Texas'
  #part_number: 'mpn'
  size_source: 'http://www.ti.com/lit/ml/mpqf391c/mpqf391c.pdf'
  ipc_class: 'qfn' # 'qfn_pull_back'
  #ipc_density: 'least' #overwrite global value for this device.
  # custom_name_format:
  body_size_x:
    minimum: 1.55
    maximum: 1.65
  body_size_y:
    minimum: 1.55
    maximum: 1.65
  body_height:
    maximum: 0.4

  lead_width:
    minimum: 0.15
    maximum: 0.25
  lead_len_V:
    minimum: 0.2
    maximum: 0.4
  lead_len_H:
    minimum: 0.4
    maximum: 0.6

  heel_reduction: 0.075

  pitch: 0.4
  num_pins_x: 4
  num_pins_y: 2