Improve Reddit text and media handling

[edwinRNDR]

Adds the preview media to the Post media. Also uses a concatenation of title and selftext for Post text.

[sokomishalov]

Hi @edwinRNDR!
Thanks for your contribution :)

I'm planning to release 0.4.0 version within a week, and one of the features will be field thumbnail in the Video class. I don't think that preview media is equal to other media of the post so I can add this functionality in the next release to prevent the implicit mixing of these data structures.
Is it ok for you?
You can watch it in this work-in-progress pull request #24.

Title and selftext concatenation looks fine to me.

[sokomishalov]

@edwinRNDR hey!
Thanks again for the contribution, your feature is available in 0.4.0 now.
I'll close this PR.

[edwinRNDR]

Ah, apologies for my late reply. But this sounds all good to me. Just one thing, the reason I added the preview images is because they seem to often contain images that are not in any other media links in the Reddit json. Thank you for considering my PR :)