Connection pool package should not define `Pool` type as an interface
since it provides single particular implementation.
Make `pool.Pool` type a struct instead of interface. Also remove
`Object`, `Container` and `Accounting` interfaces.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Define `XPrm` type for each `X` client operation which structures
parameters. Export setters of each parameterized value. Emphasize that
some parameters are required. Make the client panic when the parameters
are incorrectly set. Get rid of vadiadic call options and `CallOption`
type. Improve documentation of client behavior.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
