Create a makefile and gen directory for classes/objects

Right now, class files and objects are compiled manually into the root directory. This pull request comes with a `makefile` and a new directory `gen`. The object and class files generated by `make` are placed in `gen`. Everything in gen is ignored by git (see gen/.gitignore).

* To compile all three languages, run `make` or `make wiki` from the root directory.
* To compile (if needed) and run the tests for `java`, `c`, or `cpp`, run `make {lang}`.

You may want to move the readme instructions higher up. But, it's up to you. Also, the `c` compilation command is slightly different since I needed to add the `gcc -lm` flag. Mileage may vary.