Closes #253.

I simplified the implementation of this class a bit, and extended the unit tests to include a case that was causing problems before.
Code syntax
Fixed unused parameter
Merge pull request #254 from standage/master

Closes #253.
Fixes ill-formatted API documentation for GtSetSourceVisitor
Vanity edit
Merge pull request #257 from standage/cont

Vanity edit
Merge pull request #256 from standage/docs

Fixes ill-formatted API documentation for GtSetSourceVisitor