Switch to the Apache License v2 (python#25)

This is one of the two approved incoming PSF licenses.

Closes python#23

LICENSE

@@ -1,29 +1,13 @@
-BSD 3-Clause License
+Copyright 2017 Brett Cannon, Barry Warsaw
 
-Copyright (c) 2017, Brett Cannon
-All rights reserved.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
 
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
+http://www.apache.org/licenses/LICENSE-2.0
 
-* Redistributions of source code must retain the above copyright notice, this
-  list of conditions and the following disclaimer.
-
-* Redistributions in binary form must reproduce the above copyright notice,
-  this list of conditions and the following disclaimer in the documentation
-  and/or other materials provided with the distribution.
-
-* Neither the name of the copyright holder nor the names of its
-  contributors may be used to endorse or promote products derived from
-  this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
-FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
-SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
-OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.

flit.ini

@@ -8,8 +8,7 @@ home-page = https://importlib_resources.rtfd.io
 description-file = README.rst
 classifiers = Development Status :: 3 - Alpha
     Intended Audience :: Developers
-    License :: OSI Approved :: BSD License
+    License :: OSI Approved :: Apache Software License
     Topic :: Software Development :: Libraries
     Programming Language :: Python :: 3
 requires-python = >=3.4
-license = BSD 3-clause "New" or "Revised" License