Tag format doesn't match that of Obsidian

[jayemar]

From the Obsidian page on tag:

You can use any of the following characters in your tags:

Alphabetical letters
Numbers
Underscore (_)
Hyphen (-)
Forward slash (/) for [Nested tags](https://help.obsidian.md/Editing+and+formatting/Tags#Nested%20tags)

Tags must contain at least one non-numerical character. For example, #1984 isn't a valid tag, but #y1984 is.

Tags can't contain blank spaces.

obsidian.el currently allows plus sign, as well as numerical-only tags, neither of which are valid Obsidian tags.

Ideally, the obsidian--tag-regex could be updated to match that of Obsidan. The regex below comes close, but it will also extract tags from the middle of a string which I do not believe are valid Obsidian tags. (For example, it will extract #bar from foo#bar and treat it like a tag.)

"#[[:alnum:]_/-]*[[:alpha:]_/-]+[[:alnum:]_/-]*"