Implementation of Fraction.limit_denominator.

Remove Fraction.to_continued_fraction and
Fraction.from_continued_fraction
diff --git a/Doc/library/fractions.rst b/Doc/library/fractions.rst
index 7f6019f..adc70c6 100644
--- a/Doc/library/fractions.rst
+++ b/Doc/library/fractions.rst
@@ -46,6 +46,24 @@
    :class:`decimal.Decimal`.
 
 
+.. method:: Fraction.limit_denominator(max_denominator=1000000)
+
+   Finds and returns the closest :class:`Fraction` to ``self`` that
+   has denominator at most max_denominator.  This method is useful for
+   finding rational approximations to a given floating-point number::
+
+      >>> Fraction('3.1415926535897932').limit_denominator(1000)
+      Fraction(355, 113)
+
+   or for recovering a rational number that's represented as a float::
+
+      >>> from math import pi, cos
+      >>> Fraction.from_float(cos(pi/3))
+      Fraction(4503599627370497L, 9007199254740992L)
+      >>> Fraction.from_float(cos(pi/3)).limit_denominator()
+      Fraction(1, 2)
+
+
 .. method:: Fraction.__floor__()
 
    Returns the greatest :class:`int` ``<= self``. Will be accessible