HOWTO: Parse DETP command in geometry.g

Warning: you are entering expert territory here...
geometry.g is the module responsible for configuring geometries w/in an interactive version of starsim.  In such an interactive session, one sets up a specific geometry by calling  
starsim> DETP geom y2010 [more options]
The y2010 keyword, along with any other keywords in [more options], is parsed in geometry.g. Any keyword which matches a "Case" statement will execute the commands w/in the case statement. The syntax of the case statement is:
Case MATCH {
"mandatory comment line printed when case is evaluated";
In the event that the keyword is of the form MATCH=value, then the real*4 variable myarg will be assigned value.