Cleaner project and test execution

Properly defined the test namespace so we don't need a bootstrap.php
file - now we can simply use the vendor/autoload to run our tests.
Removed PluginCollection class

I got rid of the need to have your plugins contained in the
PluginCollection class - a simple array works just as well. Let's not
over-complicate things.
Update phpunit, composer, and gitignore

A few changes to these guys to make the project run a little more
smoothly.
Use vendor/autoload.php for loading

Updated all the examples to use vendor/autoload.php instead of our
bootstrap file, which, coincidentally, no longer exists.