Split LICENSE into two files (#15)

Currently, GitHub doesn't automatically recognize tophu's licenses,
presumably because the text of both licenses are appened to the
`LICENSE` file, causing that file to fail pattern matching.

Other dual-licensed software repos (e.g.
https://github.com/facebook/buck2) *do* have their licenses recognized
by GitHub. The trick seems to be to put the contents of each license in
a separate file.

This has the minor downside of making the top-level directory slightly
more crowded.

LICENSE → LICENSE-Apache-2.0

@@ -1,37 +1,3 @@
-This software is licensed under either the BSD-3-Clause or Apache-2.0 license. Users may
-choose which license to apply. The terms of each license are reproduced below.
-
----------------------------------------------------------------------------------------
-
-Copyright (c) 2022 California Institute of Technology ("Caltech"). U.S. Government
-sponsorship acknowledged.
-
-All rights reserved.
-
-Redistribution and use in source and binary forms, with or without modification, are
-permitted provided that the following conditions are met:
-
-* 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 Caltech nor its operating division, the Jet Propulsion Laboratory,
-  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 OWNER 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.
-
----------------------------------------------------------------------------------------
-
                                  Apache License
                            Version 2.0, January 2004
                         http://www.apache.org/licenses/

LICENSE-BSD-3-Clause

@@ -0,0 +1,26 @@
+Copyright (c) 2022 California Institute of Technology ("Caltech"). U.S. Government
+sponsorship acknowledged.
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification, are
+permitted provided that the following conditions are met:
+
+* 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 Caltech nor its operating division, the Jet Propulsion Laboratory,
+  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 OWNER 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.