Observers now limited to Controller.

Also removed a method that was now unnecessary since we're using Commons
IO, and fixed a bug that was temporarily introduced by the use of Commons
IO (the readFileToString(File) method always closes the file).
Addition text can come from a file.

Fixes #12. Also, depreciated file reading methods have been replaced with
appropriate, non-depreciated ones. The charset of files for now is assumed
to be UTF-8 (ASCII compatible). I expect that to be configurable in the
future.