Divide by zero error in calculate_frequencies()

[Ycreak]

Hi Dargones,

I was experimenting with small datasets of various meters. In the case of the glyconeus and the iambic dimeter, I used Seneca Medea 75–92 and 849-855 respectively. These verses do not have elisions, which crashes Anceps, as it tries to calculate the frequency of elisions in the given dataset. Maybe you could add a try or a small check for zero in the calculate_frequencies function in analyze.py. The error almost never occurs, and only for elisions of course, but just wanted to let you know :)