Implement support to variable STATUS_LINE inside libmodsecurity

[zimmerle]

More information about STATUS_LINE can be found at ModSecurity reference manual: https://github.com/SpiderLabs/ModSecurity/wiki/Reference-Manual

[zimmerle]

Status line is a mix between RESPONSE_STATUS and a verbose complementary for the response status. For instance: "200 ok". Although this `ok' is quite trivial to be retrieved from Apache is not that simple in other web server and it may not be needed. Therefore we are going to consider this variable as deprecated on v3. Instead the user is able to RESPONSE_STATUS which semantically will lead to almost the same functionality.