• removed unused functions from XS file
  -- reduces size of compiled objects
  
• simplified implementation of Digest::SHA object
  -- now a blessed SHAPtr ref instead of blessed array ref
  -- results in slight speed-up of OO operations
  
• streamlined underlying C source
  -- used macros to consolidate repetitive code
  
• rewrote test scripts to depend on Test rather than Test::More
  -- allows module to be checked in minimal Perl environments
  
• added compilation option for thread-safety
  -- overrides use of static arrays