Backport of PEP 3101, Advanced String Formatting, from py3k.

Highlights:
 - Adding PyObject_Format.
 - Adding string.Format class.
 - Adding __format__ for str, unicode, int, long, float, datetime.
 - Adding builtin format.
 - Adding ''.format and u''.format.
 - str/unicode fixups for formatters.

The files in Objects/stringlib that implement PEP 3101 (stringdefs.h,
unicodedefs.h, formatter.h, string_format.h) are identical in trunk
and py3k.  Any changes from here on should be made to trunk, and
changes will propogate to py3k).

Objects/stringlib/stringdefs.h

@@ -0,0 +1,27 @@
+#ifndef STRINGLIB_STRINGDEFS_H
+#define STRINGLIB_STRINGDEFS_H
+
+/* this is sort of a hack.  there's at least one place (formatting
+   floats) where some stringlib code takes a different path if it's
+   compiled as unicode. */
+#define STRINGLIB_IS_UNICODE     0
+
+#define STRINGLIB_OBJECT         PyStringObject
+#define STRINGLIB_CHAR           char
+#define STRINGLIB_TYPE_NAME      "string"
+#define STRINGLIB_PARSE_CODE     "S"
+#define STRINGLIB_EMPTY          nullstring
+#define STRINGLIB_ISDECIMAL(x)   ((x >= '0') && (x <= '9'))
+#define STRINGLIB_TODECIMAL(x)   (STRINGLIB_ISDECIMAL(x) ? (x - '0') : -1)
+#define STRINGLIB_TOUPPER        toupper
+#define STRINGLIB_TOLOWER        tolower
+#define STRINGLIB_FILL           memset
+#define STRINGLIB_STR            PyString_AS_STRING
+#define STRINGLIB_LEN            PyString_GET_SIZE
+#define STRINGLIB_NEW            PyString_FromStringAndSize
+#define STRINGLIB_RESIZE         _PyString_Resize
+#define STRINGLIB_CHECK          PyString_Check
+#define STRINGLIB_CMP            memcmp
+#define STRINGLIB_TOSTR          PyObject_Str
+
+#endif /* !STRINGLIB_STRINGDEFS_H */