Division of integers returns floor in python 2.x

[tompollard]

The default behaviour for division has changed between Python 2 and Python 3. In Python 3, dividing an integer by an integer returns a float. e.g.

In  [1]: 3/2
Out [1]: 1.5

In Python 2, the default behaviour is to return an integer (the floor of the division). e.g.

In  [1]: 3/2
Out [1]: 1

The current code does not account for this difference, so incorrect results are returned in Python 2. For example, https://github.com/MIT-LCP/wfdb-python/blob/master/wfdb/_rdann.py includes the line:

testbytes=filebytes[:(12+math.ceil(auxlen/2)),:].flatten()

[tompollard]

I think I've picked them all up, but some may have slipped past me, so we should ensure the tests look out for this issue.