Get rid of cartridge in the Picodata documentation for SQL

After supporting of CREATE and DROP SQL commands for Picodata we can totally rewrite our documentation for SQL. We must wipe out all the mentions of cartridge dynamic library, but rather describe pico.sql() interface in Picodata.

First candidates for refactoring:

1. Работа с SQL в Picodata -> Что такое Sbroad (replace with something about Picodata).
2. Пример работы с SQL Broadcaster в Picodata (totally rewrite)
3. Команды SQL (rewrite examples)