modify code to suppress or fix warnings in gcc and clang (#41)

* first fix to start branch PR

* explicit conversion from sizet to int

* Array.h and DiagonalMatrix.h

* many sizet to int conversions

* removed some unused variables and added expl overrides

* removed many unused parameters

* more typing

* even more

* last of the easy changes

OndselSolver/System.cpp

@@ -186,7 +186,7 @@ double System::maximumMass()
 double System::maximumMomentOfInertia()
 {
 	double max = 0.0;
-	for (int i = 0; i < parts->size(); i++)
+	for (int i = 0; i < (int)parts->size(); i++)
 	{
 		auto& part = parts->at(i);
 		for (int j = 0; j < 3; j++)