Changed filters to by fluent rather than array based

[dcblogdev]

This PR changes filtering from:

Xero::contacts()->get(int $page = 1, string $where = null)

to fluent methods:

->filter() methods are optional and can add multiple filters. Only filters set out in an emum are supported:

 case IDS = 'ids';
 case INCLUDEARCHIVED = 'includeArchived';
 case ORDER = 'order';
 case PAGE = 'page';
 case SEARCHTERM = 'searchTerm';
 case SUMMARYONLY = 'summaryOnly';
 case WHERE = 'where';

Usage

Xero::contacts()
->filter('page', 1)
->filter('where', 'EmailAddress=="info@abfl.com"')
->filter('where', 'ContactID==Guid("74ea95ea-6e1e-435d-9c30-0dff8ae1bd80")')
->filter('searchTerm', 'info')
->filter('includeArchived', 'false')
->filter('order', 'name')
->filter('summaryOnly', 'true')
->get();

[FortuneV13]

This is great. Please can you update the readme to use the new filter(). Thank you.