support column title string set by user

[ynishi]

• support explicit title setting.
• now, inherit papaparse json support http://papaparse.com/docs#json-to-csv
• add this style

  var csv = convert(
  header: {
  "Column1": "ColumnTitle1",
  "Column2": "ColumnTitle2"
  },
  data: [
  {
      "Column1": "foo",
      "Column2": "bar"
  },
  {
      "Column1": "abc",
      "Column2": "def"
  }]);

[ynishi]

• Props: header, dataJson

  
  Props:{
  ...
  header: {
  "Column1": "ColumnTitle1",
  "Column2": "ColumnTitle2"
  },
  data: [
  {
      "Column1": "foo",
      "Column2": "bar"
  },
  {
      "Column1": "abc",
      "Column2": "def"
  }],
  ...
  };