Move all client headers and sources to public/ directory.

public/libbacktrace/config.h

@@ -0,0 +1,22 @@
+#include <limits.h>
+#if __WORDSIZE == 64
+#  define BACKTRACE_ELF_SIZE 64
+#else
+#  define BACKTRACE_ELF_SIZE 32
+#endif
+
+#define HAVE_DLFCN_H 1
+#define HAVE_FCNTL 1
+#define HAVE_INTTYPES_H 1
+#define HAVE_LSTAT 1
+#define HAVE_READLINK 1
+#define HAVE_DL_ITERATE_PHDR 1
+#define HAVE_ATOMIC_FUNCTIONS 1
+#define HAVE_DECL_STRNLEN 1
+
+#ifdef __APPLE__
+#  define HAVE_MACH_O_DYLD_H 1
+#elif defined BSD
+#  define HAVE_KERN_PROC 1
+#  define HAVE_KERN_PROC_ARGS 1
+#endif