Added the Hash.sort_by() method which can sort hashes by a given value.

Example: hash.sort_by{|__,b| b};  # sorts the hash by value
         hash.sort_by{|a,__| a};  # sorts the hash by key

Added the Time.micro() method to get the current time of day at  microseconds precission.
Added the scripts/hash_sort.sf
Fixed the '|=' and '&=' assign operators. (aliases for '||=' and '&&=')
Other minor changes.