[UPDATE][SHELL] Add quote to variable expansions

Everyone assumes that spaces do not exist on a Linux system... This is
unfortunately not the case (although I hate having spaces in my own
files). Quoting the variables avoids running into those kind of issues.

shell/.functions

@@ -37,21 +37,21 @@ fi
 # jump directorys upwards until it hits a directory with multiple folders
 function up() {
   local d=""
-  limit=$1
+  limit="$1"
   for ((i=1 ; i <= limit ; i++))
     do
-      d=$d/..
+      d="$d/.."
     done
-  d=$(echo $d | sed 's/^\///')
+  d=$(echo "$d" | sed 's/^\///')
   if [ -z "$d" ]; then
     d=..
   fi
-  cd $d
+  cd "$d"
 }
 
 # create an directory and directly cd into it
-function mcd () {
-  mkdir -p $1
-  cd $1
+function mcd() {
+  mkdir -p "$1"
+  cd "$1"
 }