Add articles filtering

[vhood]

I suggest adding a feed article titles filter.

For example, if we have 2 articles of some feed:

Hey! Today: something happend
Good recipe ...

and the setting.json file includes something like:

"rss.feeds": [
    {
        "path": "https://rss-source.example",
        "articles": {
            "filter": "today"
        }
    }
]

the only article

Hey! Today: something happend

should be shown.