Identify hashtags like draft-js-plugins.hashtag
Effective forms:
#word
#word123
#123word
#word_123
#123_word
Invalid forms:
#123
#word#word
Identify hashtags like draft-js-plugins.hashtag
Effective forms:
#word
#word123
#123word
#word_123
#123_word
Invalid forms:
#123
#word#word