Improve rsMatrix* documentation, fix bugs

Improves the user-facing documentation.  Fix the incorrect row & column
naming on the Get/Set API.  Fix a bug where rsMatrixLoadMultiply could
not have the destination be one of the source,
e.g. rsMatrixLoadMultiply(&l, &l, &r)

Change-Id: I42207aacf4ebe815d4a79db2aaa9c44f85864696

rsMatrix3x3.cpp

diff --git a/rsMatrix3x3.cpp b/rsMatrix3x3.cpp
index 3f9a2d1..4f27fcc 100644
--- a/rsMatrix3x3.cpp
+++ b/rsMatrix3x3.cpp
@@ -46,6 +46,9 @@
 }
 
 void Matrix3x3::loadMultiply(const rs_matrix3x3 *lhs, const rs_matrix3x3 *rhs) {
+    // Use a temporary variable to support the case where one of the inputs
+    // is also the destination, e.g. left.loadMultiply(left, right);
+    Matrix3x3 temp;
     for (int i=0 ; i<3 ; i++) {
         float ri0 = 0;
         float ri1 = 0;
@@ -56,10 +59,11 @@
             ri1 += ((const Matrix3x3 *)lhs)->get(j, 1) * rhs_ij;
             ri2 += ((const Matrix3x3 *)lhs)->get(j, 2) * rhs_ij;
         }
-        set(i, 0, ri0);
-        set(i, 1, ri1);
-        set(i, 2, ri2);
+        temp.set(i, 0, ri0);
+        temp.set(i, 1, ri1);
+        temp.set(i, 2, ri2);
     }
+    load(&temp);
 }
 
 void Matrix3x3::transpose() {