generic UQFN-10 inspired by USB3740 (replaces #717)

This required updating the generator to handle differently sized leads for vertical and horizontal direction.

datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/00001725D.pdf script PR: https://github.com/pointhi/kicad-footprint-generator/pull/149

parameters:

UQFN-10_1.3x1.8mm_P0.4mm:
  device_type: 'UQFN'
  size_source: 'http://ww1.microchip.com/downloads/en/DeviceDoc/00001725D.pdf (Page 9)'
  ipc_class: 'qfn' # 'qfn_pull_back'
  body_size_x:
    nominal: 1.3
    tolerance: 0
  body_size_y:
    nominal: 1.8
    tolerance: 0
  lead_width:
    minimum: 0.15
    maximum: 0.25
  lead_len_V:
    minimum: 0.35
    maximum: 0.45
  lead_len_H:
    minimum: 0.45
    maximum: 0.55

  heel_reduction: 0.05 #necessary to reach 0.2mm clearance between vertical and horizontal pads

  pitch: 0.4
  num_pins_x: 3
  num_pins_y: 2

UQFN-10_1.6x2.1mm_P0.5mm:
  device_type: 'UQFN'
  size_source: 'http://ww1.microchip.com/downloads/en/DeviceDoc/00001725D.pdf (Page 12)'
  ipc_class: 'qfn' # 'qfn_pull_back'
  body_size_x:
    nominal: 1.6
    tolerance: 0
  body_size_y:
    nominal: 2.1
    tolerance: 0
  lead_width:
    minimum: 0.2
    maximum: 0.3
  lead_len_V:
    minimum: 0.35
    maximum: 0.45
  lead_len_H:
    minimum: 0.6
    maximum: 0.7

  # heel_reduction: 0.05 #for relatively large EP pads (increase clearance)

  pitch: 0.5
  num_pins_x: 3
  num_pins_y: 2