make github recognize license, add authors.md, clarify shared copyright (#513)

* Update LICENSE

* add authors.md, update license

* update whatsnew

Author: wholmgren

AUTHORS.md

@@ -0,0 +1,32 @@
+About the Copyright Holders
+===========================
+
+*   Copyright (c) 2013, Sandia National Laboratories
+
+    Sandia National Laboratories developed pvlib python based on code in
+    PVLib MATLAB.
+
+*   Copyright (c) 2014-2018, pvlib python Development Team
+
+    The pvlib python Development Team is the collection of developers of the
+    pvlib python project.
+
+Full credits for pvlib python contributors can be found in the documentation.
+
+Our Copyright Policy
+====================
+
+pvlib python uses a shared copyright model. Each contributor maintains copyright
+over their contributions to pvlib python. However, it is important to note that
+these contributions are typically only changes to the repositories. Thus,
+the pvlib python source code, in its entirety, is not the copyright of any single
+person or institution. Instead, it is the collective copyright of the
+entire pvlib python Development Team. If individual contributors want to maintain
+a record of what changes/contributions they have specific copyright on,
+they should indicate their copyright in the commit message of the change
+when they commit the change to the pvlib python repository.
+
+License
+=======
+
+pvlib python is distributed under a 3-clause BSD license.

LICENSE

@@ -1,7 +1,6 @@
-Copyright (c) 2013, Sandia National Labs
-All rights reserved.
+BSD 3-Clause License
 
-Copyright (c) 2014-2016, PVLIB Python Developers
+Copyright (c) 2013-2018, Sandia National Laboratories and pvlib python Development Team
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without modification,

docs/sphinx/source/whatsnew/v0.6.0.rst

@@ -65,6 +65,9 @@ Bug fixes
   (:issue:`493`)
 * Fix ``pvlib.irradiance.klucher`` output is different for Pandas Series vs.
   floats and NumPy arrays. (:issue:`508`)
+* Make GitHub recognize the license, add AUTHORS.md, clarify shared copyright.
+  (:issue:`503`)
+
 
 Documentation
 ~~~~~~~~~~~~~