Implement `transaction.end()`

[Taylor Troesh]

The following example is listed in the official docs:

const transaction = client.createTransaction(
  "partially_rolled_back_transaction",
);
await transaction.savepoint("undo");
await transaction.queryArray`TRUNCATE TABLE DONT_DELETE_ME`; // Oops, wrong table
await transaction.rollback("undo"); // Truncate is rolled back, transaction continues
await transaction.end();

It's in the docs, but doesn't seem to exist in the code.

Without .end(), we can't reuse connections, which is pretty important for many applications:

const client = await pool.connect();
while (true) {
  const tx = client.createTransaction(`example-tx`);
  tx.queryArray(`...`);
  await tx.commit();
  await tx.end(); // doesn't exist
  n++;
}

If the intended design is to reconnect to the pool, maybe we should update the docs?

[Steven Guerrero]

There is indeed a mistake in the docs making a mention of an end method which doesn't exist, however you don't need to look for a close method in order to close a transaction

The commit method will take care of closing the transaction and releasing the client per https://doc.deno.land/https://deno.land/x/postgres@v0.15.0/mod.ts/~/Transaction#commit and the docs (unless the commit is specified to be chained)

I'll close this issue once the docs are updated to remove references to the close method