Option to restrict hashtags to word boundary

[nicodh]

In a string like "test#foo" the #foo is parsed as hashtag which is unexpected behaviour imho.

It's definitely wrong in a string like example.com#foo where #foo is a separate link (maybe related to #516 though)

Even if there is no strict definition "Some platforms may require the # to be preceded with a space"

Gihub for example: not a hashtag#516

I tried to fix that in the plugin but that seems not possible. (?)