Rely on the interface rather than the config in updateInterface.

For consistency.
Add brief comments to testConfigHandler.

Explains ConfigHandler usage.
Remove usage of karaskel from LineCollection.

Since we are only using a small subset of the functions karaskel
provides, we don't need to drag in the whole library.
Add namespace to the aegisub-motion libraries.
Add Line class and move line operations out of LineCollection.
Use FFI to determine the user's operating system.