#256 Automatically create source/build directories

[Dan Smith]

By default, projects contain sources and classes in the same tree
(which is probably rooted in the project file's directory). Other IDEs
automatically create source and build directories, and help to insure
that files are put in the right place. Dr. Wong would like to see an
option to mimic this behavior. Ideally, users shouldn't need to do
anything to set up their file system hierarchies. At the very least, an
option should allow a "src"/"source" and "built"/"classes" directory to
be created whenever a new project is defined, and the project's build
directory should be set appropriately.