Make BCD.reduced more accurate
Implement Integer.prepend
Implement Integer ctor for a number string

 - adjusted Integer.prepend to be more accurate
 - fixed a bug in the BCD ctor
   the size to initialize the data sink was incorrectly calculated
 - fixed a bug in the BCD ctor
   beta was being initialized incorrectly
 - fixed a bug in BCD.halve
   the processing of the string "11" was not setting the carry over
 - fixed BCD.odd - bad logic
 - fixed BCD.reduced - bad logic