Initial implementation of agent generation.

This is hardcoded to expect some files in the lib directory in the working directory of the program, obviously a temporary solution for while i was working on it. @pdaian, can you please have the installer put these files together in a predictable location? (BaseAspect.aj  MANIFEST.MF  aspectjrt.jar  aspectjtools.jar  aspectjweaver.jar  rt.jar) from @owolabileg's [build-agent archive](http://fsl.cs.illinois.edu/images/6/6d/Build-agent.tar.gz).

This adds the --agent option, where the result of
`javamop --agent directory1 directory2 file1.mop file2.mop -n mopAgent`
reads all the files in directory1 and directory2 and uses file1.mop and file2.mop and produces a file `mopAgent.jar` that can be used as a java agent with existing java code.

This still needs some work (deleting intermediate generated files, and refactoring the code), but I'm putting this up now in case @owolabileg, @grosu, or @pdaian have comments.
```if(! aopAjc.exists()){...}```? If you have future plans for this code path, it's probably best to document such in a TODO. Writing like this just makes it harder to read.