Puzzlerbot must ignore its name in `text included to back quotes`

[skapral]

Steps to reproduce:

1. Try creating a puzzle from the following comment:

@puzzlerbot FYI

The list of priviledged users, who can manage the `@puzzlerbot`, must be a configurable option.

Subj.

Expected result:

• A puzzle created with title "The list of priviledged users, who can manage the @puzzlerbot, must be a configurable option." and body "Subj."

Actual result:

• A puzzle created with title "Subj." and empty description

Explanation: since the puzzlerbot is mentioned in the first and second line, they both were classified as controlling paragraphs. "Subj." line became a title then.