LISTEN/NOTIFY funcionality

Signed-off-by: chandr-andr (Kiselev Aleksandr) <chandr@chandr.net>

Author: chandr-andr

docs/components/components_overview.md

@@ -8,6 +8,7 @@ title: Components
 - `Connection`: represents single database connection, can be retrieved from `ConnectionPool`.
 - `Transaction`: represents database transaction, can be made from `Connection`.
 - `Cursor`: represents database cursor, can be made from `Transaction`.
+- `Listener`: object to work with [LISTEN](https://www.postgresql.org/docs/current/sql-listen.html)/[NOTIFY](https://www.postgresql.org/docs/current/sql-notify.html) functionality, can be mode from `ConnectionPool`.
 - `QueryResult`: represents list of results from database.
 - `SingleQueryResult`: represents single result from the database.
 - `Exceptions`: we have some custom exceptions.

docs/components/listener.md

@@ -6,7 +6,7 @@ title: Listener
 
 ## Usage
 
-There two ways of using `Listener` object:
+There are two ways of using `Listener` object:
 - Async iterator
 - Background task