factorize implementation of standard real unary math functions, and add acos, asin
diff --git a/doc/snippets/Cwise_acos.cpp b/doc/snippets/Cwise_acos.cpp
new file mode 100644
index 0000000..34432cb
--- /dev/null
+++ b/doc/snippets/Cwise_acos.cpp
@@ -0,0 +1,2 @@
+Array3d v(0, sqrt(2.)/2, 1);
+cout << v.acos() << endl;