Treat punctuation as hashtag delimiters

[mojodna]

Unicode ranges for punctuation are simpler than creating a Unicode-aware word class, so delimit on non-words.

Fixes #4398

[bhousel]

Thanks @mojodna! Looks pretty good.. I merged it and then made 2 other little changes in 8f82caf:

• I removed the _, so hashtags can have underscores in them
• I changed the quantifier from * to + so it would match 1 or more instead of 0 or more. The original would detect a single lonely "#" character, even in cases where the hashtags string was empty.

[mojodna]

Thanks. I was being spacey when I put that together; too much of a hurry