Read DNA from a 2bit file where each base is encoded in 2bit 
        (4 bases per byte).
        
        Parameters
        ----------
        d:
        l : tuple
            Location tuple
        
        Returns
        -------
        list
            Array of base chars

def _read2bit(d, l, offset=False):
        """
        Read DNA from a 2bit file where each base is encoded in 2bit 
        (4 bases per byte).
        
        Parameters
        ----------
        d:
        l : tuple
            Location tuple
        
        Returns
        -------
        list
            Array of base chars
        """
        
        s = l.start - 1
        
        ret = bytearray([0] * l.length) #[]
        
        if offset:
            bi = s // 4
        else:
            bi = 0
        
        for i in range(0, l.length):
            block = s % 4
            
            if block == 0:
                v = (d[bi] >> 6)
            elif block == 1:
                v = (d[bi] >> 4)
            elif block == 2:
                v = (d[bi] >> 2)
            else:
                v = d[bi]
                
                # Reached end of byte so we are moving into the next byte
                bi += 1
            
            # Only care about the lowest 2 bits
            v &= 3
            
            ret[i] = DNA_UC_DECODE_DICT[v]
                
            s += 1
            
        return ret