added where::asLiteral

[malteriesch]

Added method to add more 'free-form' where conditionals:

$this->query
    ->setTable('user')
    ->where()
    ->asLiteral("(username is not null and status=:status)")
    ->notEquals('name', '%N%');

which will result in the query

SELECT user.* FROM user WHERE (username is not null and status=:status) AND (user.name <> :v1)

[scrutinizer-notifier]

The inspection completed: 1 updated code elements

[nilportugues]

Nice addition and great to see test pass! I'm merging this