create a module for dynamic classloading

[radai-rosenblatt]

we have code for defining new classes att runtime in fast-avro.
we also use net.openhft:compiler in some of our unit tests to do similar things, but that has issues running under the most recent JDKs due to its use of raw reflection to define classes
we need to take our CompilerHelper class and expand it to allow replacing all these use cases.

desirable features:

1. no reflective access to avoid issues on modern JREs (via subclassing ClassLoader, see https://docs.oracle.com/javase/9/docs/api/java/lang/ClassLoader.html)
2. create a new ClassLoader (backed by a folder), have all compilation and classloading happen from tthis CL.
3. write out all generated source to be compiled as well as generated class files to disk for debuggablity