Sr-api

* Fixed type where you couldn't use the `greyscale` filter
* Removed `spin` from filter method, unsure how it even got there

* You can now get the url from methods that return an `Image` object by casting the object to `str`

* Fixed passing a key in `Client`

* Added "key" to `Client.__slots__`

* Renamed `Client.beta()` to `Client.filter()` since its no longer a beta feature
* Added `whale` and `pikachu` to `Client.get_image()`
* Added `invertgreyscale`, `brightness`, `threshold`, `red`, `green` & `blue` to `Client.filter()`
* Added `Client.youtube_comment()`
* Added `Client.view_color()`
* Added `Client.rgb_to_hex()`
* Added `Client.hex_to_rgb()`
* Added `Client.get_joke()`
* Added support for using premium. Provide your premium key in the Client init like `client = sr_api.Client("key here")`. Dont provide a key if you dont have one.
* Removed `Client.get_pikachu()` which is now available in `Client.get_image()`

* Fixed issue with beta endpoint