Updated CodeConventions (markdown)

CodeConventions.md

@@ -10,11 +10,12 @@ Lua
 - Name variables for what they are, don't include type markers in them, i.e. *do not* use Hungarian notation.
 - Nice to have: sort your requires alphabetically (OCD!)
 - Only comment if it's something complicated/non obvious. Keep in mind that comments increase file size, which increases the amount of RAM required to run your program!
+- If you have to validate arguments, use the built-in `checkArg` method. Homogenous error messages are a good thing! Its usage is `checkArg(n, value, type1, ...)`, where `n` is the number of the argument, `value` is the value of the argument and `type1` and so on are the allowed types for the argument, as retrieved via `type(value)`. The number is used in the error message like so: "bad argument #n (type1 expected, got type(value))". So for example, to require the first argument to be a number you'd do `checkArg(1, arg, "number")`.
 
 Bad:
 ```lua
 function f(sArg1 , ... )
-    print(sArg1)
+   assert(type(sArg1)== "string", "me wants a strign!")
     if sArg1 then
         local nResult = 1
         --do some more stuff
@@ -29,7 +30,7 @@ end
 Good:
 ```lua
 function f(arg1, ...)
-  print(arg1)
+  checkArg(1, arg1, "string")
   if arg1 then
     local result = 1
     -- We extrapolate the b-spline of the non-euclidean space to