Aiodogstatsd

- Updated documentation: described why 9125 port used by default, 16
- Added [`Starlette`](https://www.starlette.io) framework integration helpers (middleware), #15
- Fixed futures initialization. From this time futures always initialized in the same event loop, 15
- Added [documentation](https://gr1n.github.io/aiodogstatsd), #18

- Fixed `MTags` type to be a `Mapping` to avoid common invariance type-checking errors, 14 by JayH5

- Added sample rate as class attribute, for setting sample rate class-wide, 11 by aviramha
- Added timer context manager for easily timing events, 12 by aviramha
- Added Python 3.8.* support, 7

- Fixed `AIOHTTP` middleware to catch any possible exception, 6
- Fixed `AIOHTTP` middleware to properly handle variable routes, 8

- Fixed `AIOHTTP` graceful shutdown, 5 by Reskov

- **Breaking Change:** Send time in milliseconds in middlewares, 3 by eserge