Add video date

[bors-ltd]

Hi, yt-fts is a great tool, but I always find myself needing a date in the results, at least for sorting results chronologically.

So I made the changes, quick and dirty (picking the "upload_date" field), but it gets the job done. Would you be interested in a proper pull request? I think not because it would change the schema again, and I read in another issue you considered it stable.

I'm OK with maintaining my changes on top of the main line for my own usage.

[NotJoeMartinez]

@bors-ltd you're right about me considering the schema "stable" However I still want to be able to make changes such as an upload_date column in the Videos table and a last_updated column in the Channels table.

My biggest concern isn't necessarily adding breaking changes, it's adding breaking changes that could modify users' existing database in unpredictable ways or fail without providing hints that they are using a legacy version of the tool.

I planned to add a metadata table to the db that stores the yt-fts versions it is compatible with and I want to do that before making any more changes to the schema. Please still make the PR for the compatible version you have. Thanks.

[bors-ltd]

Oops, I opened #144 but it's not linked to that issue. I guess I'm a bit rusty with Github.