bytevectors, 2/8/16-base integer literals

0) New type of cell: bytevector; read/write support:

    ;>> (define hello #u8(72 101 108 108 111 0))
    ;>> (secd-type hello)
       bvect

    ;>> hello
       #u8(#x48 #x65 #x6c #x6c #x6f #x00 )

1) introduced radix-prefix syntax for integer literals:
    ;>> #x100           ;; base 16
       256
    ;>> #b1010          ;; base 2
       10
    ;>> #d42            ;; required by R6RS, R7RS
       42
2) negative integer literals:
    ;>> -1
       -1

tmp