add foam material

gpkitmodels/GP/materials/foam.py

@@ -0,0 +1,16 @@
+from gpkit import Model, parse_variables
+
+class Foam(Model):
+    """ Foam material properties
+
+    Variables
+    ---------
+    rho         0.036       [g/cm^3]        foam density
+
+    LaTex Strings
+    -------------
+    rho             \\rho_{\\mathrm{foam}}
+
+    """
+    def setup(self):
+        exec parse_variables(Foam.__doc__)