Move binpac code into the main Zeek repository

This is based on commit 48f75b5f6415fe9d597e3e991cec635b1bc400dc from
the binpac repository.

tools/binpac/lib/binpac_bytestring.cc

@@ -0,0 +1,15 @@
+#define binpac_regex_h
+
+#include "binpac_bytestring.h"
+
+#include <stdlib.h>
+
+namespace binpac {
+
+std::string std_string(bytestring const* s) { return std::string((const char*)s->begin(), (const char*)s->end()); }
+
+int bytestring_to_int(bytestring const* s) { return atoi((const char*)s->begin()); }
+
+double bytestring_to_double(bytestring const* s) { return atof((const char*)s->begin()); }
+
+} // namespace binpac