release 0.4

Happy 30th birthday, MPW!

This includes a bunch of fixes since the previous version. Other enhancements:

• -f flag disables parsing the Startup script
• builtin Catenate command
• builtin Execute command
• builtin Quit command
• builtin Exit command
• subshells!
• known to build/run on linux and solaris

OS X build included below. Put mpw-shell and mpw-make somewhere in your $PATH (like /usr/local/bin) and etc/Startup in your $HOME/mpw/ directory.