nt2int changes

Fixed bugs because of C strings. In short, nt2int converts 'A' to 0, which when considered as a string is '\0' which is the string terminating character. Thus the integer "strings" were being truncated at the first 'A'. This was fixed by changing nt2int, and augmenting the Unique object.

Added iseq and length to Unique object...
Unique.iseq: holds the index sequence in a char array.
Unique.length: the length of the sequences (strlen of seq).