Move ksw2 files to a subdirectory and add license

ext/README.md

@@ -60,3 +60,10 @@ License: See xxhash.c
 Homepage: https://github.com/mateidavid/zstr
 Commit used: 755da7890ea22478a702e3139092e6c964fab1f5
 License: See zstr/LICENSE
+
+
+## ksw2
+
+https://github.com/lh3/ksw2
+https://raw.githubusercontent.com/lh3/ksw2/06b2183b0f6646d82f2e3f5884008a1b4582f5b5/ksw2.h
+https://raw.githubusercontent.com/lh3/ksw2/06b2183b0f6646d82f2e3f5884008a1b4582f5b5/ksw2_extz2_sse.c

ext/ksw2/LICENSE.txt

@@ -0,0 +1,24 @@
+The MIT License
+
+Copyright (c) 2018-     Dana-Farber Cancer Institute
+              2017-2018 Broad Institute, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.