Include LZ4 README and LICENSE.

ext/lz4/LICENSE

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+LZ4 Library
+Copyright (c) 2011-2016, Yann Collet
+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.
+
+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.

ext/lz4/README.md

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+LZ4 - Library Files
+================================
+
+The directory contains many files, but depending on project's objectives,
+not all of them are necessary.
+
+#### Minimal LZ4 build
+
+The minimum required is **`lz4.c`** and **`lz4.h`**,
+which will provide the fast compression and decompression algorithm.
+
+
+#### The High Compression variant of LZ4
+
+For more compression at the cost of compression speed,
+the High Compression variant **lz4hc** is available.
+It's necessary to add **`lz4hc.c`** and **`lz4hc.h`**.
+The variant still depends on regular `lz4` source files.
+In particular, the decompression is still provided by `lz4.c`.
+
+
+#### Compatibility issues
+
+In order to produce files or streams compatible with `lz4` command line utility,
+it's necessary to encode lz4-compressed blocks using the [official interoperable frame format].
+This format is generated and decoded automatically by the **lz4frame** library.
+In order to work properly, lz4frame needs lz4 and lz4hc, and also **xxhash**,
+which provides error detection.
+(_Advanced stuff_ : It's possible to hide xxhash symbols into a local namespace.
+This is what `liblz4` does, to avoid symbol duplication
+in case a user program would link to several libraries containing xxhash symbols.)
+
+
+#### Advanced API 
+
+A more complex `lz4frame_static.h` is also provided.
+It contains definitions which are not guaranteed to remain stable within future versions.
+It must be used with static linking ***only***.
+
+
+#### Using MinGW+MSYS to create DLL
+
+DLL can be created using MinGW+MSYS with the `make liblz4` command.
+This command creates `dll\liblz4.dll` and the import library `dll\liblz4.lib`.
+The import library is only required with Visual C++.
+The header files `lz4.h`, `lz4hc.h`, `lz4frame.h` and the dynamic library
+`dll\liblz4.dll` are required to compile a project using gcc/MinGW.
+The dynamic library has to be added to linking options.
+It means that if a project that uses LZ4 consists of a single `test-dll.c`
+file it should be linked with `dll\liblz4.dll`. For example:
+```
+    gcc $(CFLAGS) -Iinclude/ test-dll.c -o test-dll dll\liblz4.dll
+```
+The compiled executable will require LZ4 DLL which is available at `dll\liblz4.dll`. 
+
+
+#### Miscellaneous 
+
+Other files present in the directory are not source code. There are :
+
+ - LICENSE : contains the BSD license text
+ - Makefile : script to compile or install lz4 library (static or dynamic)
+ - liblz4.pc.in : for pkg-config (make install)
+ - README.md : this file
+
+[official interoperable frame format]: ../doc/lz4_Frame_format.md
+
+
+#### License 
+
+All source material within __lib__ directory are BSD 2-Clause licensed.
+See [LICENSE](LICENSE) for details.
+The license is also repeated at the top of each source file.