Added addErrorOnLine and addWarningOnLine

Specifying line number instead of $stackPtr when adding errors
enables to write custom sniffs using [nikic/php-parser](https://github.com/nikic/PHP-Parser).

Using PHP Parser greatly simplifies writing sniffs when there's no need to inspect whitespaces. For example when I want to check if use clausules at the beginning of the file are alphabetically ordered or whether all exceptions are used via fully qualified name.