add ability to ignore paths during model serialization

[spencerschrock]

Summary

Adds the ability to pass in one or more ignore paths to exclude files and/or directories during model serialization.

Closes #196

Release Note

NONE

Documentation

NONE

[spencerschrock]

I still need to polish some of the docstrings and add a few more test scenarios, but at a high level does this make sense?

Specifically, the introduction of ignore_paths to Serializer.serialize. There is at least one alternative here: accepting a function to do the filtering, which would have more flexibility but also be more verbose to setup for callers.

[mihaimaruseac]

Let's go with the list for now, and migrate to function later when we need to add that functionality