Added script which checks cross-document links

Added a script which reads all .md files and checks if the links are valid.
Also corrected two mistakes found by this script.

Documentation/check_links.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+homedir=$(pwd)
+
+for file in $(find . -name '*.md')
+do
+    cd "$(dirname $file)"
+    for i in `grep -o '\[.*\]([^#].*[.]md)' $(basename $file)| sed -e 's/\[.*\](\(.*\))/\1/'`
+    do
+        if [ ! -f $i ]
+        then
+            echo "Link $i in $file is not correct!"
+        fi
+    done
+    cd "$homedir"
+done