Expand copyright to include babylon/acorn authors, add AUTHORS file

AUTHORS

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+Direct contributors to the Sucrase project:
+Alan Pierce
+
+Sucrase contains a modified fork of Babylon, which itself was forked from Acorn.
+Babel and Babylon are copyright 2014-2018 Sebastian McKenzie
+See https://babeljs.io/team for a list of contributors to the Babel project.
+
+List of Acorn contributors:
+Adrian Rakovsky
+Alistair Braidwood
+Andres Suarez
+Aparajita Fishman
+Arian Stolwijk
+Artem Govorov
+Brandon Mills
+Charles Hughes
+Conrad Irwin
+David Bonnet
+Forbes Lindesay
+Gilad Peleg
+impinball
+Ingvar Stepanyan
+Jesse McCarthy
+Jiaxing Wang
+Joel Kemp
+Johannes Herr
+Jürg Lehni
+keeyipchan
+Kevin Kwok
+krator
+Marijn Haverbeke
+Martin Carlberg
+Mathias Bynens
+Mathieu 'p01' Henri
+Max Schaefer
+Max Zerzouri
+Mihai Bazon
+Mike Rennie
+Nick Fitzgerald
+Oskar Schöldström
+Paul Harper
+Peter Rust
+PlNG
+r-e-d
+Rich Harris
+Sebastian McKenzie
+zsjforcn

LICENSE

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 The MIT License (MIT)
 
-Copyright (c) 2017 Alan Pierce
+Copyright (c) 2012-2018 various contributors (see AUTHORS)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal