Support for paint endpoint

[CoderHam]

Sample client

import cohere
import os
import base64

API_KEY = os.getenv('COHERE_API_KEY')
cohere.COHERE_API_URL = "https://dev.api.cohere.ai/"
co = cohere.Client(API_KEY)

# x = co.whisper(file_paths=<INSERT_FILE_PATH>)
x = co.image(<INSERT_PROMPT>)
with open("image.png", "wb") as f:
    f.write(base64.b64decode(x.image))

[robertkozin]

Looks good so far, you can request my review when you're done and I'll approve it