Computes the bnum2-th power of bnum1 using a simple binary algorithm.
For more information see GNU MP 4.1

Prototype
   bnum BigNum.pow( bnum1 , bnum2 )

Parameters
   bnum1 and bnum2
      Positive big numbers.

Return Value
   This function returns a big number which represents the bnum2-th power of bnum1

Remarks
   bnum1 and bnum2 must be created before function call.

Example
   
require( "BigNum.lua" )

a = BigNum.new( "25" )
b = BigNum.new( "2" )
c = BigNum.pow( a , b )
print( "POW = " .. c )
   
Output
   
POW = 625