Add scripted DFN-8 3x3mm 1.7x2.05mm EP for IX4426-27-28

This replaces #831

The script stuff is included in my larger scripting pull request https://github.com/pointhi/kicad-footprint-generator/pull/149

Script parameters:

DFN-8-1EP_3x3mm_P0.65mm_EP1.7x2.05mm:
  device_type: 'DFN'
  #manufacturer: 'man'
  #part_number: 'mpn'
  size_source: 'http://www.ixysic.com/home/pdfs.nsf/www/IX4426-27-28.pdf/$file/IX4426-27-28.pdf'
  # ipc_class: 'qfn' # 'qfn_pull_back'
  #ipc_density: 'least' #overwrite global value for this device.
  body_size_x:
    nominal: 3
    tolerance: 0
  body_size_y:
    nominal: 3
    tolerance: 0
  lead_width:
    nominal: 0.3
    tolerance: 0.05
  lead_len:
    nominal: 0.4
    tolerance: 0.05

  EP_size_x: 1.7
  EP_size_y: 2.05
  # EP_paste_coverage: 0.65
  EP_num_paste_pads: [2, 2]
  # heel_reduction: 0.1 #for relatively large EP pads (increase clearance)

  pitch: 0.65
  num_pins_x: 0
  num_pins_y: 4
  #chamfer_edge_pins: 0.25
  #pin_count_grid:
  #pad_length_addition: 0.5
  #suffix: '_PullBack'
  #include_suffix_in_3dpath: 'False'
  #include_pad_size: 'fp_name_only' # 'both' | 'none' (default)