Since June 2015, use of the word lit has exploded on Twitter. Here's some recent examples.
My Year is starting off lit af👌🏼 ...but is gonna be TD by Monday morning
Jason got lit last night. Was the show for at least half the snapchat stories this morning.
When you and bae both lit and give each other that look
The @lovihatibot Twitterbot routinely finds it in searches for "I love the word [X]" and "I hate the word [X]", in fact it's the third most hated) and eighth most loved over 30 days, and fourth most hated and 10th most loved in all of 2015. That's a lot of love and hate for a little word, it can't be random babble to cause such a reaction.
What does lit mean here?
Where does it come from and when was it first used?
Was there a single person or event which popularised it, and when was it? Or if it's an older word, what accounts for its recent popularity?