Add wxLZMAInputStream for decompressing data in XZ format

No compression support yet.

interface/wx/lzmastream.h

@@ -0,0 +1,60 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/lzmastream.h
+// Purpose:     LZMA [de]compression classes documentation
+// Author:      Vadim Zeitlin
+// Created:     2018-03-29
+// Copyright:   (c) 2018 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+/**
+    @class wxLZMAInputStream
+
+    This filter stream decompresses data in XZ format.
+
+    XZ format uses LZMA2 algorithm for compression used for .xz files and is
+    similar to GZip or BZip2 format. Notice that it is different from, and
+    incompatible with, 7z archive format even although it uses the same
+    compression algorithm.
+
+    To decompress contents of standard input to standard output, the following
+    (not optimally efficient) code could be used:
+    @code
+    wxFFileInputStream fin(stdin);
+    wxLZMAInputStream zin(fin);
+    wxFFileOutputStream fout(stdout);
+    zin.Read(fout);
+
+    if ( zin.GetLastError() != wxSTREAM_EOF ) {
+        ... handle error ...
+    }
+    @endcode
+
+    @library{wxbase}
+    @category{archive,streams}
+
+    @see wxInputStream, wxZlibInputStream
+
+    @since 3.1.2
+*/
+class wxLZMAInputStream : public wxFilterInputStream
+{
+public:
+    /**
+        Create decompressing stream associated with the given underlying
+        stream.
+
+        This overload does not take ownership of the @a stream.
+    */
+    wxLZMAInputStream(wxInputStream& stream);
+
+    /**
+        Create decompressing stream associated with the given underlying
+        stream and takes ownership of it.
+
+        As with the base wxFilterInputStream class, passing @a stream by
+        pointer indicates that this object takes ownership of it and will
+        delete it when it is itself destroyed.
+     */
+    wxLZMAInputStream(wxInputStream* stream);
+};