Syntactic sugar for aiomysql

I successfully use your library in several projects.
I propose a solution to simplify the work with the library.

```python
import asyncio
from CshLib.conn import MySQL

class MySQLModules(MySQL):
user = 'stat'
password = 'bh0020'
db = 'modules'

async def test():
async with MySQLModules() as conn:
async with conn.cursor() as cur:
await cur.execute("SELECT Count(*) FROM modules.modules;")
records = await cur.fetchone()
print(records)

asyncio.run(test())
```

MySQL class code

```python
import aiomysql

class MySQL:
host = '127.0.0.1'
port = 3306
user = ''
password = ''
db = ''

async def __aenter__(self) -> aiomysql.connection:
self.conn = await aiomysql.connect(
host=self.host,
port=self.port,
user=self.user,
password=self.password,
db=self.db
)
return self.conn

async def __aexit__(self, exc_type, exc_val, exc_tb):
self.conn.close()
```