ENH: expand VectorSpaceOps to include copy_n/fill_n methods

- similar to what std::copy_n and std::fill_n would do, except with
  templated loops. This allows compile-time transcribing with loop
  unrolling. For example,

     vector vec1 = ..., vec2 = ...;

     FixedList<scalar, 6> values;

     VectorSpaceOps<3>::copy_n(vec1.begin(), values.begin());
     VectorSpaceOps<3>::copy_n(vec2.begin(), values.begin(3))

     // do something with all of these values

STYLE: make start index of VectorSpaceOps optional

ENH: add clamped begin(int) versions to FixedList as per UList

applications/test/vectorTools/Test-vectorTools.cxx

@@ -0,0 +1,76 @@
+#include "vector.H"
+#include "IOstreams.H"
+#include "vectorTools.H"
+#include "unitConversion.H"
+
+using namespace Foam;
+
+
+void test(const vector& a, const vector& b, const scalar tolerance)
+{
+    Info<< "Vectors " << a << " and " << b
+        << " are (to tolerance of " << tolerance << "): ";
+
+    if (vectorTools::areParallel(a, b, tolerance))
+        Info<< " parallel ";
+
+    if (vectorTools::areOrthogonal(a, b, tolerance))
+        Info<< " orthogonal ";
+
+    if (vectorTools::areAcute(a, b))
+        Info<< " acute ";
+
+    if (vectorTools::areObtuse(a, b))
+        Info<< " obtuse ";
+
+    Info<< ", angle = " << vectorTools::degAngleBetween(a, b);
+
+    Info<< endl;
+}
+
+
+int main()
+{
+    vector a(vector::uniform(1));
+    vector b;
+    b.fill(2);
+
+    test(a, b, 0.0);
+    test(a, b, VSMALL);
+    test(a, b, SMALL);
+    test(a, b, 1e-3);
+    test(a, b, 1e-1);
+
+    a = vector(1,0,0);
+    b = vector(0,2,0);
+
+    test(a, b, 0.0);
+    test(a, b, VSMALL);
+    test(a, b, SMALL);
+    test(a, b, 1e-3);
+    test(a, b, 1e-1);
+
+    a = vector(1,0,0);
+    b = vector(-1,0,0);
+
+    test(a, b, 0.0);
+    test(a, b, VSMALL);
+    test(a, b, SMALL);
+    test(a, b, 1e-3);
+    test(a, b, 1e-1);
+
+    a = vector(1,0,0);
+    b = vector(-1,2,0);
+
+    test(a, b, 0.0);
+    test(a, b, VSMALL);
+    test(a, b, SMALL);
+    test(a, b, 1e-3);
+    test(a, b, 1e-1);
+
+    Info<< "\nEnd\n" << nl;
+
+    return 0;
+}
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //