Timeout: set a limit on long running statements.
Classpath: add to the runtime classpath.
Startup script paths: run specified initialization scripts.
Startup script: run a specified block of code on startup.
Imports most of the standard java libraries as the jshell tool does.
These include java.{util,io,math,net}.* and
java.util.{concurrent,prefs,regex}.*
Additionally introductory support for 2 simple magic commands '%sh' and
'%%writefile' for running a shell command and writing to a file.
* Compilation errors don't print a stack trace but rather explain the
error, print the problematic source lines, and highlight the specific
error region.
* Incomplete source doesn't print a stack trace but rather the
incomplete lines and a message notifying the user that the code is
incomplete.
* Evaluation exceptions don't print 'EvalException' as the exception
name but instead the class name of the underlying exception that the
exception wraps.
