add get_segments method to collections.LineCollection

[toddrjen]

collections.LineCollection has a set_segments method that lets you set the vertices of the line segments in the collection. However, it has no corresponding get_segments method. This adds the method.

This version implements the suggestions from pelson on the last version of this pull request.

[pelson]

Hmmm. There are some strange commits here. Would you mind "squashing" your commits into one and git push origin +get_segments you branch.

[toddrjen]

Commits are squashed

[pelson]

Thanks @toddrjen - I see no reason not to merge (so have done so).

Good stuff!