Cleaning Up Left-Over 'Origin' References

When I first broke source properties into a class, I called that class 'Origin',
then ended up renaming it to 'SourceProperty' before I checked it in. Some of
the variables and methods that were related to 'origins' did not get renamed
to 'source properties' along the way, so this is cleaning up some remaining
variables and methods as I was making some other changes.

Related to #14.
Tests for Single-Character Properties

Added two tests for the ReflectionSourceProperty to ensure that it works with single-character
fields and methods, since these were an edge case that I'd written down during the implementation
as a potential concern.

They worked, so this is additional test code with no changes to the reflection source property.

Related to #14.