Syzygy tablebases

Adds support for Syzygy tablebases to Stockfish.  See
the Readme for information on using the tablebases.

Tablebase support can be enabled/disabled at the Makefile
level as well, by setting syzygy=yes or syzygy=no.

Big/little endian are both supported.

No functional change (if Tablebases are not used).

Resolves #6

src/syzygy/tbprobe.h

@@ -0,0 +1,16 @@
+#ifndef TBPROBE_H
+#define TBPROBE_H
+
+namespace Tablebases {
+
+extern int TBLargest;
+
+void init(const std::string& path);
+int probe_wdl(Position& pos, int *success);
+int probe_dtz(Position& pos, int *success);
+bool root_probe(Position& pos, Value& TBScore);
+bool root_probe_wdl(Position& pos, Value& TBScore);
+
+}
+
+#endif