sql: support prepared statements

[Totktonada]

First, it allows to collect information about data types in a response without actual execution (and also get parsed info re input parameters). Second, it allows to don't resend SQL request text each time, just new input parameters.

Documentation: tarantool/doc#1055 and https://www.tarantool.io/en/doc/latest/dev_guide/internals/box_protocol/.

The database API part is here: #176.