Accepting different kinds of zettel formats

[tevino]

Currently zkviz requires the zettel to be formatted like this:

• Filename: YYYYMMDDHHMMSS TITLE.md
• The YYYYMMDDHHMMSS is unique

or it finds nothing, say this case for example.

It would be great if there's an option to choose another format of zettel:

> zkviz --zettel-format [TS-TITLE|ID]

Users that are not using a timestamp-based ID could benefit from zkviz too.

Here's my setup: http://tevinzhang.com/digital-zettelkasten/

TL;DR:

• Filename: ID.md
• Title: in the file starting with #

The current implementation is called asTS-TITLE since it is a combination of a timestamp and title, the format I described above is ID, the names may vary, here's just a proposal to add a new flag indicating different formats.

I could submit a PR if that's needed.