Find a rational approximation to a given number.
[FIXME: unfinished]
Uses continued series.
(see .... mathworld.com ... 
for more information on continued series).
Algorithm from
http://home.earthlink.net/~mrob/pub/math/numbers-2.html
:
 If you want to generate a whole series of numerators and denominators, use an algorithm like this:

 
   (given: X = number to be converted) 
   N = 1 
   D = 0 
   N1 = 0 
   D1 = 1 
   repeat until satisfied: 
     let XI = integer part of X 
     let X = fractional part of X 
     let X = 1 / X 
     let N2 = N1 
     let N1 = N 
     let N = N1 * XI + N2 
     let D2 = D1 
     let D1 = D 
     let D = D1 * XI + D2 
     print "New approximation: ", N, "/", D 
   end repeat