Add more test for reliability

[TTWNO]

We should have tests for any type of event which can be passed to odilia/src/events/mod.rs::dispatch, which is currently around 175.
We absolutely need tests to detect what changes are made to state, making sure that certain other parts of state are not affected, etc.

This would essentially be integration testing, since the State requires an active SSIP connection, DBus connection, configurations from files, etc.

I'm putting this in for 0.2.0, since I think focusing on reliability this early will pay off in the long-run.

Here's a list of current functions which can be dispatched to, there should be at least one test per function here:

• Add code coverage report so we can get an idea of how much code is covered with our tests.
• document::load_complete
• cache::add_accessible
• cache::remove_accessible
• object::state_changed (this should at least have one case for both adding and removing a state)
• object::text_caret_moved
• object::text_changed
• object::children_changed

[TTWNO]

The hot fix applied between v0.1.0 and 0.1.1 is the perfect example of an issue which could have been caught by testing more code.

The bug that was solved in the patch had to do with not updating the cursor caret position anywhere within the Odilia code base. If we would have tested sending a test environment to the primary dispatch() function, we likely would have had better luck tracking down the issue faster, and without releasing a broken version to the public.

This strengthens my resolve to have better testing infrastructure.

[TTWNO]

Blocked on odilia-app/atspi#82; planning to merge before the end of the month, hopefully.