switch cardinality labels' positions

[msladecek]

Issue

see #54

Summary

Cardinality labels on relationships labels are drawn in a different order compared to common ER schemes, which causes confusion when interpreting the diagram.

Solution

Flip cardinality labels for ForeignKey-type relations.

Before

After

In my opinion, this better represents the relationship:

• One or more people can be born in the same location
• A person has at most one known birth location

closes #54

[DylanModesitt]

will this ever be merged?