New Halton sequence code

Changed to Blair's formula-based halton sequence computations.  Much
faster for big numbers.  Prior to this, Halton was computed by brute
force conversion to base and reversal of digits.  With this change, no
longer needed baseb2dec and dec2baseb.
Updated BAS to use square, rather than rectangle

Changed BAS routine to use a square over the study area, rather than a
rectangle.  this is in line with the theory in the paper.