Arbitrary website support

[dumbasPL]

Would be nice to have the option to specify an arbitrary URL and an expression to match the version from the returned web page.

We could just make it simple and use REGEX (yes, I know, "parsing" HTML with regex...) or use a proper HTML parser and let the user specify a CSS selector/xpath that points to an element that contains the version. If the content of that element changes we assume a new version has been released.

Importing an RSS feed is nice and all, but those are becoming pretty rare nowadays.

A generic JSON one would also be nice, just a simple URL and a path to the key that contains the version.