We don't really need Credentials (it's all about private key) and ClientPlant
(it's a pool). NewEphemeralKey moved temporarily to pool.
Signed-off-by: Roman Khimov <roman@nspcc.ru>
Renamed PoolBuilderOptions to BuilderOptions and PoolBuilder to Builder
because usages of them with prefix pool.* in other packages stutter.
Signed-off-by: Angira Kekteeva <kira@nspcc.ru>