Scripted wson and wqfn for LDC1312 etc (replaces #1257)

Replaces #1257

symbols: https://github.com/KiCad/kicad-symbols/pull/1366 script: https://github.com/pointhi/kicad-footprint-generator/pull/258

http://www.ti.com/lit/ds/symlink/ldc1312.pdf#page=59

WSON-12-1EP_4x4mm_P0.5mm_EP2.6x3mm:
  device_type: 'WSON'
  library: Package_SON
  size_source: 'http://www.ti.com/lit/ds/symlink/ldc1312.pdf#page=62'
  ipc_class: 'qfn' #'qfn' | 'qfn_pull_back'
  body_size_x:
    minimum: 3.9
    maximum: 4.1
  body_size_y:
    minimum: 3.9
    maximum: 4.1
  body_height:
    minimum: 0.8
    maximum: 1

  lead_width:
    minimum: 0.2
    maximum: 0.3
  lead_len:
    minimum: 0.3
    maximum: 0.5

  EP_size_x:
    nominal: 2.6
    tolerance: 0.1
  EP_size_y:
    nominal: 3
    tolerance: 0.1
  EP_num_paste_pads: [2, 2]

  thermal_vias:
    count: [3, 3]
    drill: 0.2
    paste_via_clearance: 0.1
    EP_paste_coverage: 0.75
    paste_avoid_via: False

  pitch: 0.5
  num_pins_x: 0
  num_pins_y: 6

WQFN-16-1EP_4x4mm_P0.5mm_EP2.6x2.6mm:
  device_type: 'WQFN'
  size_source: 'http://www.ti.com/lit/ds/symlink/ldc1312.pdf#page=59'
  ipc_class: 'qfn' # 'qfn_pull_back'
  body_size_x:
    minimum: 3.9
    maximum: 4.1
  body_size_y:
    minimum: 3.9
    maximum: 4.1
  body_height:
    maximum: 0.8

  lead_width:
    minimum: 0.2
    maximum: 0.3
  lead_len:
    minimum: 0.3
    maximum: 0.5

  EP_size_x:
    nominal: 2.6
    tolerance: 0.1
  EP_size_y:
    nominal: 2.6
    tolerance: 0.1
  EP_num_paste_pads: [2, 2]

  thermal_vias:
    count: [3, 3]
    drill: 0.2
    paste_via_clearance: 0.1
    EP_num_paste_pads: [2, 2]
    EP_paste_coverage: 0.75
    paste_avoid_via: False

  pitch: 0.5
  num_pins_x: 4
  num_pins_y: 4