Update changelog

Author: jackc

CHANGELOG.md

@@ -1,17 +1,20 @@
-# 4.0.0 (Prerelease)
+# 4.0.0 (Release candidate)
 
-v4 is a major release with many significant changes.
+v4 is a major release with many significant changes. The most significant are included below.
 
 * Simplified establishing a connection with a connection string.
 * All potentially blocking operations now require a context.Context. The non-context aware functions have been removed.
 * OIDs are hard-coded for known types. This saves the query on connection.
 * Context cancellations while network activity is in progress is now always fatal. Previously, it was sometimes recoverable. This led to increased complexity in pgx itself and in application code.
 * Go modules are required.
-* Errors are now implemented in the Go 1.13 style. Tests for specific error types must use `As` or `Is`.
-* `Rows` is now an interface.
+* Errors are now implemented in the Go 1.13 style.
+* `Rows` and `Tx` are now interfaces.
 * The connection pool as been decoupled from pgx and is now a separate, included package (github.com/jackc/pgx/v4/pgxpool).
 * pgtype has been spun off to a separate package (github.com/jackc/pgtype).
 * pgproto3 has been spun off to a separate package (github.com/jackc/pgproto3).
+* Logical replication support has been spun off to a separate package (github.com/jackc/pglogrepl).
 * Lower level PostgreSQL functionality is now implemented in a separate package (github.com/jackc/pgconn).
-* Replication support has been temporarily removed. It will be implemented in a separate package.
 * Tests are now configured with environment variables.
+* Conn has an automatic statement cache by default.
+* Batch interface has been simplified.
+* QueryArgs has been removed.