Update src/Former/Checkable.php

Added support for repopulating grouped checkbox values from POST and value arrays

Multiple checkboxes with 'name[]' passes the name attribute to the POST variable without brackets

The current code did not take this into account and was checking the POST variable using 'name[]' instead of 'name'

The current code also checked the checkbox value against a single POST variable, however, using 'name[]' will cause the POST variable to be an array, so I added an in_array check.