Count hashes (or other run of chars) at start of line

        >>> x = Mark2Slide()
        >>> x.hash_count('### hello')
        3

        >>> x = Mark2Slide()
        >>> x.hash_count(' hello', ' ')
        1

def hash_count(self, line, pound=None):
        """ Count hashes (or other run of chars) at start of line

        >>> x = Mark2Slide()
        >>> x.hash_count('### hello')
        3

        >>> x = Mark2Slide()
        >>> x.hash_count(' hello', ' ')
        1

        """
        if pound is None:
            pound = '#'
            
        count = 0
        for c in line:
            if c != pound:
                break
            count += 1

        return count