Add image aspect ratio for Bluesky

[JoelOtter]

Hey @snarfed, here's my attempt at adding the image aspect ratio. Please tear it apart with extreme prejudice, I haven't written Python for many months now.

I added Pillow as a dependency to Granary - do we need to add it to Bridgy too? It wouldn't work locally unless I installed it there but I probably am misunderstanding how the local installation stuff in Pip works.

Fixes #843

[JoelOtter]

Oh this is going to annoy the tests isn't it. Can we use a real image URL for the test data?

[snarfed]

Hah, yes. I think what you'd do is add a small image file to the tests/testdata/ directory, then update test_create_with_media to read it in as binary an return its bytes in the mock requests.get response:

granary/granary/tests/test_bluesky.py

Lines 3481 to 3485 in c29dd72

	@patch('requests.post')
	@patch('requests.get')
	def test_create_with_media(self, mock_get, mock_post):
	mock_get.return_value = requests_response(
	'pic data', headers={'Content-Type': 'my/pic'})

[JoelOtter]

That works, thanks!

[snarfed]

Test looks great! Thank you!

[snarfed]

Looking good. One last minor nit, and then add this to the changelog in the readme, and I think we're set!

[JoelOtter]

Have added to README but please reword or move if it's wrong or in the wrong place :)

[snarfed]

Looks great! Thank you!

Are you stlil set up to run this locally? It'd be nice to try interactively and see if it actually works.

[JoelOtter]

Yes I've already used it to post things :) before and after:

[snarfed]

Awesome! Thank you for testing! OK, merging now, really psyched for this, thanks again for the contribution.