Returns the bit value at offset in the string value stored at key.
When offset is beyond the string length, the string is assumed to be a contiguous space with 0 bits. When key does not exist it is assumed to be an empty string, so offset is always out of range and the value is also assumed to be a contiguous space with 0 bits.
@return
@integer-reply: the bit value stored at offset.
@examples
SETBIT mykey 7 1
GETBIT mykey 0
GETBIT mykey 7
GETBIT mykey 100