Reformat LICENSE so github sees it as BSD-3-Clause. (#4181)
Reformat LICENSE so github sees it as BSD-3-Clause. (#4181)

This changes LICENSE text to the standard BSD-3-Clause text.
	The wording is almost identical, with only "copyright holders
	and contributors" replacing "Michael Stapelberg and contributors"
	in the license text.
Airblader/i3-original,Airblader/i3,i3/i3,Airblader/i3-original,Airblader/i3-original,stapelberg/i3,stapelberg/i3,Airblader/i3-original,Airblader/i3,Airblader/i3,i3/i3,stapelberg/i3,Airblader/i3-original,i3/i3,i3/i3,stapelberg/i3,Airblader/i3