Fix various typos

Found via `codespell -q 3 -S ./rtdata/languages -L activ,alph,ba,bloc,bord,chang,childs,currentry,dof,dum,fo,hist,inout,invers,lonly,makro,ois,pres,preserv,portugues,rady,reall,redy,struc,tbe,thre,trough,vart,vekto`

rtengine/iimage.h

@@ -1858,7 +1858,7 @@ class IImage : virtual public ImageDimensions
 public:
 
     virtual ~IImage() {}
-    /** @brief Returns a mutex that can is useful in many situations. No image operations shuold be performed without locking this mutex.
+    /** @brief Returns a mutex that can is useful in many situations. No image operations should be performed without locking this mutex.
       * @return The mutex */
     virtual MyMutex& getMutex () = 0;
     virtual cmsHPROFILE getProfile () const = 0;