update according to new caching behaviour

Author: xWTF

documentation/Prepared-Statements.md

@@ -13,9 +13,12 @@ connection.execute('select 1 + ? + ? as result', [5, 6], (err, rows) => {
 // close cached statement for 'select 1 + ? + ? as result'. noop if not in cache
 connection.unprepare('select 1 + ? + ? as result');
 ```
+Note that `connection.execute()` will cache the prepared statement for better performance, remove the cache with `connection.unprepare()` when you're done.
 
 ## Manual prepare / execute
 
+Manually prepared statements doesn't comes with LRU cache and SHOULD be closed using `statement.close()` instead of `connection.unprepare()`.
+
 ```js
 connection.prepare('select ? + ? as tests', (err, statement) => {
   // statement.parameters - array of column definitions, length === number of params, here 2
@@ -27,9 +30,9 @@ connection.prepare('select ? + ? as tests', (err, statement) => {
     // -> [ { tests: 3 } ]
   });
 
-  // do not use statement.close(), use connection.unprepare() to remove lru cache properly.
+  // don't use connection.unprepare(), it won't work!
   // note that there is no callback here. There is no statement close ack at protocol level.
-  connection.unprepare('select ? + ? as tests');
+  statement.close();
 });
 ```
 Note that you should not use statement after connection reset (`changeUser()` or disconnect). Statement scope is connection, you need to prepare statement for each new connection in order to use it.

promise.d.ts

@@ -140,9 +140,6 @@ export function createConnection(
 export function createPool(config: PoolOptions): Pool;
 
 export interface PreparedStatementInfo {
-  /**
-   * Close the prepared statement. This method DO NOT REMOVE the statement cache, and should only be used internally. Use {@link Connection.unprepare} instead when you've done with prepared statement.
-   */
   close(): Promise<void>;
   execute(parameters: any[]): Promise<[RowDataPacket[][] | RowDataPacket[] | OkPacket | OkPacket[] | ResultSetHeader, FieldPacket[]]>;
 }