This commit add the title of milestone in string representation of Milestone class.
This modification improve readbility of milestone instances.
Before:
```python
>>> repo.get_milestone(number=1)
Milestone(number=1)
```
After:
```python
>>> repo.get_milestone(number=1)
Milestone(title='Milestone Example', number=1)
```
This is a minor thing. It’s a convention, not a rule (obviously)—but it’s also a best practice.
Many text editors look for this kind of comment as the first line—or second line, if there is a shebang (the `#!/usr/bin/env python`, or whatever else)—and make use of this to determine the file’s encoding.
Michell Stuttgart