i9482: Improve documentation concerning norm functionality.

Added forkfour Latex command to math js support.

Split cv::norm documentation between the cv::norm and its overload, to make things clearer

Corrected some typos and cleaned up grammar.

Result is clearer documentation for the norms.

Work pending...

doc/mymath.sty

@@ -28,7 +28,14 @@
   #3 & \mbox{#4}\\
   #5 & \mbox{#6}\\
   \end{array} \right.}
-
+\newcommand{\forkthree}[8]{
+  \left\{
+  \begin{array}{l l}
+  #1 & \mbox{#2}\\
+  #3 & \mbox{#4}\\
+  #5 & \mbox{#6}\\
+  #7 & \mbox{#8}\\
+  \end{array} \right.}
 \newcommand{\vecthree}[3]{
 \begin{bmatrix}
  #1\\