- now compiled to their own sub-directory of the build directory
- only can see #include's in their own utility/ folders
and the core (building core.a again).
Also changed the APIs of the compilation functions somewhat (e.g. execAsynchronously no longer returns anything; it just throws a RunnerException on any error).
Still need to better handle errors in #include files; right now, the error is interpreted as being at the line where the #include happens, not within the header file.