gyp support for exiv2node

binding.gyp

{
  'targets': [
    {
      'target_name': 'exiv2',
      'sources': [
        'exiv2node.cc'
      ],
      'xcode_settings': {
        'OTHER_CFLAGS': [
          '<!@(pkg-config --cflags exiv2)',
          '-fcxx-exceptions'
        ],
      },
      'cflags': [
        '<!@(pkg-config --cflags exiv2)'
      ],
      'libraries': [
        '<!@(pkg-config --libs exiv2)'
      ],
      'ldflags': [
        '<!@(pkg-config --libs exiv2)'
      ]
    }
  ]
}