Add support for bot.chat(id) and deprecate bot.send*

The Bot API 2.1 update added support for retrieving information about a specific chat. This allows to do something like this:

``` python
bot.chat(12345).name
```

Because of that, all the `send*` methods are now useless and can be deprecated, because you can do:

``` python
bot.chat(12345).send("Test")
```
