Return string at current position + length.
        If trim == true then get as much as possible before eos.

def get_length(self, length, trim=0, offset=0):
        """Return string at current position + length.
        If trim == true then get as much as possible before eos.
        """
        if trim and not self.has_space(offset + length):
            return self.string[self.pos + offset:]
        elif self.has_space(offset + length):
            return self.string[self.pos + offset:self.pos + offset + length]
        else:
            return ''