Advanced header handling

[gharibi]

Currently the header attribute is supposed to be an array composed of the list of headers. In reality, header should have a field and an alias. This is quite important because the order of items in an object for the exportable are not necessarily the same and this cause a mismatch between the header and the rows.

The header has to be defined as follows:

headers: [{
    name: 'header_1',
    alias: 'header 1 alias',
    flex: 1
  },{
    name: 'header_2',
    alias: 'header 2 alias',
    flex: 1
  },
    . . . 
  {
    name: 'header_n',
    alias: 'header n alias',
    flex: 1
  }]

Since the current version of library is in production, it is not possible to simply shut the old versions down. In other words, there must be a backward-compatible solution. Which means it should be designed in a way, not to affect the current users.

[gharibi]

This feature is implemented in version 3.3.1.