Wit

Added encoding for special characters in url param strings

Upgrading to latest API version!
Check it out: [`20200513`](https://wit.ai/docs/http/20200513#get__message_link).

Added `session_id` to context in `messenger.py` (thanks davidawad)

The most important change is the removal of `.converse()` and `.run_actions()`. Follow the migration tutorial [here](https://github.com/wit-ai/wit-stories-migration-tutorial), or [read more here](https://wit.ai/blog/2017/07/27/sunsetting-stories).

Breaking changes

- `converse` and `run_actions` are removed
- updated and added new examples that leverage the /message API

- `message` now takes an optional `context` as second parameter
- `converse` and `run_actions` are deprecated
- `interactive` now calls `message`
- Python 3 compatibility (future imports)

- added a `speech()` method to send audio files to the API (thanks willywongi)