Building GUIs on macOS

To compile the EGSnrc Qt graphical user interfaces on macOS:

1. Install homebrew with the following command: /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
2. Use homebrew to install qt4: brew install cartr/qt4/qt
3. Find out the path to the Qt installation directory: brew info qt | grep Cellar
4. Define a corresponding QTDIR environment variable: export QTDIR=/path/to/qt/
5. Go to $HEN_HOUSE/gui/egs_gui and issue the make command
6. Go to $HEN_HOUSE/gui/egs_inprz and issue the make command
7. Go to $HEN_HOUSE/egs++/view and issue the make command